A roulette wheel contains 38 numbers of which 18 are red, 18 are black and 2 are green. When the wheel is spun it is equally likely to land on any of the 38 numbers, and successive spins are independent. The wheel is spun twice. Find the probability that the ball lands on red both times, giving your answer correct to 4 decimal places.

Model answer

0,2244

Also accepted: 0.2244, 81/361, 0,224, 0.224, 0,22, 0.22

Explanation

P(\text{red on one spin})=\dfrac{18}{38}=\dfrac{9}{19}

. The spins are independent, so

P(\text{red twice})=\dfrac{9}{19}\times\dfrac{9}{19}=\dfrac{81}{361}=0.2244

Derived from ZIMSEC Statistics Paper 4, November 2011, Q1

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