O-LevelMathematicsProbability4024/21 · Oct/Nov 2017 · Q47 Marks
Adam has a bag containing 9 balls, numbered from 1 to 9.
- (a)Adam takes a ball at random from the bag and replaces it. Find the probability that the ball has an odd number.[1]
- (b)(i)Adam takes a ball from the 9 balls in the bag, notes the number and replaces it. He then takes a second ball from the bag, notes the number and replaces it. Work out the probability that both numbers are odd.[1]
- (b)(ii)Work out the probability that one number is odd and the other is even.[2]
- (c)Adam now takes two balls from the 9 balls in the bag, without replacement. Work out the probability that the two numbers are either both odd or both even.[3]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.
- [1] 5/9 oe
- [1] 25/81 oe
- [2] M1 for (their 5/9) × (9-their5)/9 soi or (their 5/9) × 4/9 × 9/9
- [2] 40/81 oe
- [3] M2 for 5/9 * 4/8 + 4/9 * 3/8 or M1 for 4/9 * 3/8 or 5/9 * 4/8
- [3] 4/9 oe nfww
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