The Algebra Weaver
Algebraic Probability → Forming & Solving Quadratics
Panel A — The Algebra Weaver
Drag the slider to change the number of red balls. Watch P(Red, Red) update live.
P(Red, Red) — Live
Panel B — Logic Track
Phase 1 — The Anchor
The Core Rule
P(A then B, without replacement) = P(A) × P(B after A has been removed). The denominator shrinks by 1.
What changes?
You have 6 red balls and 5 blue balls. Total = 11. Pick 2 without replacement.
P(Red, Red) =
Examiner Trap
Don't read fractions carelessly — after the first pick, BOTH the numerator (what's left) AND denominator (total) change.
Panel C — Dynamic Solver
Quadratic Probability — Mark SchemeSetup the Probability
A bag has x orange sweets and 3 yellow sweets. Two sweets are picked without replacement.
All Steps
Syllabus Bridge: This type of question appears on Paper 2H (calculator allowed). Show all algebraic working — the calculator only helps you verify the quadratic's roots.
Edexcel 4MA1 · Specification 6.3 D · Applied Probability · Gen Z Study
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