Official papers

Official Specimen Paper 1 · Q7

Paper 1Probability

A bag contains nn red balls, nn yellow balls, and nn blue balls.

One ball is selected at random and not replaced.

A second ball is then selected at random and not replaced.

Each ball is equally likely to be chosen.

The probability that the two balls are not the same colour is

An−13n−1\dfrac{n-1}{3n-1}
B2n−23n−1\dfrac{2n-2}{3n-1}
C2n3n−1\dfrac{2n}{3n-1}
D(n−1)327(3n−1)3\dfrac{(n-1)^3}{27(3n-1)^3}
E3(n−1)3n−1\dfrac{3(n-1)}{3n-1}
Fn327(3n−1)3\dfrac{n^3}{27(3n-1)^3}

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