Probabilities from Venn regions
Read disjoint Venn region counts, include the whole universal population and distinguish marginals, overlap, union, outside and exactly-two events.
Exam scope and assessment notes
The first five lessons are shared Foundation work inherited by Higher; the final four are additional Higher trees, simple conditioning and applications. State the actual random mechanism, equally likely elementary outcomes, complete sample spaces and event membership. Distinguish independence from replacement and mutual exclusivity, observed relative frequency from theoretical probability, and expected frequency from a guaranteed count. Retain every ordered without-replacement history and its remaining contents. Conditional probabilities use the conditioning population; an empty condition is undefined. Inverse object counts are nonnegative integers in the original positive-denominator model. Written reasoning and assumptions still need human review; no marks or mastery are awarded. Specialist and formal-assessment approval remain pending. This is Issue2 linear4MA1; November2026/June2027 and regional-centre eligibility differ from modular awards. Literal Book1 HandlingData1/2/3 and Hub tags are navigation only; no Book2 tag or probability chapter/Hub body is verified. Keep map228–242/proof229–243/next244, map303/proof304–328/next329 and map398–428/proof397/summary426/next428 separate. Missing explicit Hub tags A/B/F/J stay missing. The common elementary two-coin model is not claimed as a novel model. Statistical-measures and diagram prerequisites do not themselves establish probability coverage.
Before you begin
- set language and Venn regions
- PR1–PR2
- whole-population totals
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
An unconditional probability is requested from a two-set Venn diagram. Which population forms the denominator?
What you will learn
- Identify intersection, union, exactly-one and outside regions in supplied Venn diagrams.
- Sum original mutually disjoint region counts once and divide by the stated whole population.
- Handle zero intersections and a clearly labelled three-set example as chosen breadth, without inferring probabilities from drawn overlap area.
A supplied two-set Venn diagram has A-only 8, both 5, B-only 7 and outside 4. One population member is chosen uniformly. Find P(A), P(B), P(A and B), P(neither) and P(exactly one of A/B). Show the selected original Venn regions for each event and state the universal-set denominator.
Enter the original physical identities, ordered outcomes, selected populations, weights, observed counts and actual geometry yourself. No space, history, support, denominator, rate, count, unknown proposal or probability is filled. A recorded representation is an attempt, not a correctness result.
Original givens and my literal probability work
Original supplied information
regions
- Aonly
- 8
- AB
- 5
- Bonly
- 7
- outside
- 4
selection
one uniformly chosen population memberSupplied atomic regions (schematic areas)
- Aonly: 8
- AB: 5
- Bonly: 7
- outside: 4
No requested event is highlighted. These are symbolic population regions; clicks never create Cartesian work points or calculate a denominator.
The original physical labels, given weights and stated mechanism are supplied. No completed sample space, tree, event selection, total, relative frequency, expected count, unknown count or requested probability is filled. Counts determine masses; drawn circle areas and tree lengths do not.
Blue supplied diagrams are schematic; amber records are actual learner work; purple is dirty retained work; dashed work is unready. Native clipping does not clamp, snap or repair points. Exact keyboard tokens and numeric-only free inverse coordinates are separate: a finite inverse click remains actual raw work even when exact-token bounds later reject it. The finite tool uses coordinates±1,000,000, up to40 tree nodes/81 terminals/4 branches,100 grid cells or weights. These are tool limits. No numerical agreement, written-text presence, drawn tree, sample space or reference proves reasoning, grants marks/mastery, or supplies teacher/specialist/formal-assessment or book-body approval.
Select my favourable and conditioning populations
No actual representation is recorded.
The question’s event names are A; B; AB; neither; exactlyOne. Enter an event row and its actual favourable/conditioning populations yourself. The original replacement or independence mechanism remains the supplied question; the interface never generates remaining counts or conditional weights.
No current explicit planar target is selected. Grid identities, event memberships, row indices, scalar weights and ordered histories use their own symbolic fields; none becomes a fake x/y coordinate.
My quantities, conclusions and explanation
Use the original physical integer-count domain; inadmissible roots remain explicit only where requested.
Keep the original event support, probability/conditioning assumptions and requested format. No denominator or answer is inserted.
Keep the original event support, probability/conditioning assumptions and requested format. No denominator or answer is inserted.
Keep the original event support, probability/conditioning assumptions and requested format. No denominator or answer is inserted.
Keep the original event support, probability/conditioning assumptions and requested format. No denominator or answer is inserted.
Keep the original event support, probability/conditioning assumptions and requested format. No denominator or answer is inserted.
A nonblank explanation is an attempt for human review, not approval of reasoning.
These original finite cases are self-checks, not automatic marking, mastery, teacher/specialist/formal-assessment or unavailable book-body approval. Equally likely physical outcomes, independence, replacement and comparable experimental conditions must be justified from each original question. An empty conditioning population is undefined, not probability zero. Expected counts are model predictions, not guaranteed observations. No statistics or modular credit is inferred.
Start with disjoint regions
A Venn diagram places members according to which named sets contain them. Each smallest non-overlapping region has its own count. The universal set includes every region inside the boundary, including the part outside all the circles. Add those disjoint counts once to find the whole population before calculating an unconditional probability.
A region label describes membership, not the size of its drawn area. Circle areas and overlap shapes are usually schematic. Use the supplied counts and the stated uniform selection of a population member. A missing region count is unknown unless other explicit information determines it; an empty region has the actual count zero and must not be silently invented.
Select the correct regions for the event
A set event includes every region lying inside that set, including its intersections with other sets. Both means the intersection. Neither means the region outside both named sets. Exactly one includes the separate parts but excludes the shared part. Mark those original regions so the event numerator can be checked before dividing by the universal total.
An or event includes every member in at least one named set. The overlap belongs to the union once, although it belongs to each separate marginal count. Handle zero intersections explicitly: if the shared region is empty, the two events are mutually exclusive. That geometric membership statement does not by itself justify any unrelated claim about independence.
Extend the same counting to three sets
With three sets, distinguish regions belonging to one, exactly two and all three sets. A marginal such as A includes A-only, its two pair-only regions and the triple region. Exactly two includes the pair-only regions and excludes the triple intersection. At least one includes all regions except the outside region, with every member counted once.
After forming an event count, divide by the same lawful whole-population denominator for an unconditional question. Check that the event is a subset of that population and that complementary counts add to the total. The three-set example is supporting practice in the same Venn method; it is not an extra official lettered requirement or evidence that drawn areas encode probabilities.
Sources for this lesson
- Pearson Mathematics A linear specification · Issue2 · Foundation printed24–25/physical30–31; Higher printed39/physical45; inheritance printed27/physical33
- Pearson2026/2027 entry manual · centre regions physical3; Mathematics A physical25
- Pearson second-edition modular book/Hub map · literal navigation only · physical4,6,7
Pause and explain
A-only has 3 members, the intersection 2, B-only 4 and outside 6. What is P(A or B) for a uniform population selection?
Worked example
A supplied two-set Venn diagram has A-only 8, both 5, B-only 7 and outside 4. One population member is chosen uniformly. Find P(A), P(B), P(A and B), P(neither) and P(exactly one of A/B). Show the selected original Venn regions for each event and state the universal-set denominator.
Show the worked solution
- Keep the supplied universal boundary and original disjoint Venn counts. Select the regions for each requested event before adding the whole-population denominator; the drawing’s areas are not weights.
- The whole population is 24, including the outside region. Count each region once.
- A contains A-only+AB and B contains B-only+AB, giving P(A)=13/24 and P(B)=1/2; P(AB)=5/24.
- Neither uses the outside region, giving 1/6. Exactly one uses A-only+B-only, giving 5/8.
Answer Universal total 24. P(A)=13/24, P(B)=1/2, P(A and B)=5/24, P(neither)=1/6, P(exactly one)=5/8. Select A-only+both for A, B-only+both for B, both for the intersection, outside for neither, and the two non-overlap parts for exactly one.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A supplied two-set Venn diagram has A-only 6, both 4, B-only 10 and outside 5. One population member is chosen uniformly. Find P(A), P(B), P(A and B), P(neither) and P(exactly one of A/B). Show the selected original Venn regions for each event and state the universal-set denominator.
Give me a hint
Write the disjoint region sum for the universal total, then mark only the original regions belonging to each requested event.
Compare my reasoning
- Keep the supplied universal boundary and original disjoint Venn counts. Select the regions for each requested event before adding the whole-population denominator; the drawing’s areas are not weights.
- The whole population is 25, including the outside region. Count each region once.
- A contains A-only+AB and B contains B-only+AB, giving P(A)=2/5 and P(B)=14/25; P(AB)=4/25.
- Neither uses the outside region, giving 1/5. Exactly one uses A-only+B-only, giving 16/25.
Universal total 25. P(A)=2/5, P(B)=14/25, P(A and B)=4/25, P(neither)=1/5, P(exactly one)=16/25. Use the original selected regions and include the outside 5 in the denominator.
Look for these in your work
- Use the whole universal set as denominator.
- Include overlap in each marginal but not twice in a union.
- Distinguish exactly-one, both and neither.
A supplied two-set Venn diagram has A-only 9, both 0, B-only 6 and outside 5. One population member is chosen uniformly. Find P(A), P(B), P(A and B), P(neither) and P(exactly one of A/B). Also find P(A or B) and state whether A and B are mutually exclusive. Show the selected original Venn regions for each event and state the universal-set denominator.
Give me a hint
Write the disjoint region sum for the universal total, then mark only the original regions belonging to each requested event.
Compare my reasoning
- Keep the supplied universal boundary and original disjoint Venn counts. Select the regions for each requested event before adding the whole-population denominator; the drawing’s areas are not weights.
- The whole population is 20, including the outside region. Count each region once.
- A contains A-only+AB and B contains B-only+AB, giving P(A)=9/20 and P(B)=3/10; P(AB)=0.
- Neither uses the outside region, giving 1/4. Exactly one uses A-only+B-only, giving 3/4. The intersection is empty, so A and B are mutually exclusive and their union is 3/4.
Universal total 20. P(A)=9/20, P(B)=3/10, P(A and B)=0, P(neither)=1/4, P(exactly one)=3/4, P(A or B)=3/4. The intersection is empty, so A and B are mutually exclusive.
Look for these in your work
- Use the whole universal set as denominator.
- Include overlap in each marginal but not twice in a union.
- Distinguish exactly-one, both and neither.
A supplied three-set Venn diagram has A-only 4, B-only 5, C-only 3, AB-only 2, AC-only 1, BC-only 4, ABC 3 and outside 2. Find P(A), P(B), P(C), P(exactly two sets), P(at least one set) and P(no set). Show the actual selected regions for each. One member of the stated population is chosen uniformly.
Give me a hint
Write the disjoint region sum for the universal total, then mark only the original regions belonging to each requested event.
Compare my reasoning
- Keep the supplied universal boundary and original disjoint Venn counts. Select the regions for each requested event before adding the whole-population denominator; the drawing’s areas are not weights.
- The eight disjoint region counts total 24. A has 4+2+1+3=10; B has 5+2+4+3=14; C has 3+1+4+3=11.
- The marginal probabilities are 10/24=5/12, 14/24=7/12 and 11/24. Exactly two sets selects only 2+1+4=7, giving 7/24.
- At least one set includes every region except outside: 22/24=11/12. No set is 2/24=1/12. The triple region is excluded from exactly two, not counted three times.
Universal total 24. P(A)=5/12, P(B)=7/12, P(C)=11/24, P(exactly two)=7/24, P(at least one)=11/12, P(no set)=1/12. Exactly two selects AB-only+AC-only+BC-only and excludes ABC; at least one includes all seven inside regions once.
Look for these in your work
- Show the selected disjoint regions.
- Separate exactly-two from at-least-two.
- Include the outside region in the total.
Common mistakes
- Omitting the outside population from the denominator.
- Adding marginal set counts and double counting their shared region.
- Including the triple region in exactly two sets.
What can you explain now?
How do exactly two sets and at least two sets differ in a three-set Venn diagram?
Compare with the explanation
Exactly two excludes the triple region; at least two includes it once.
Select the disjoint pair-only regions first, then decide whether the stated condition also admits membership in all three sets.
After trying it yourself, choose your next review. This is your self-assessment.
Your review choice appears on Today. Sign in to sync it across devices.
Make it stick
Explain the denominator and the selected regions for a marginal, intersection, union, outside and exactly-two event.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.