Question

Page 8 of 16

Megan has a bag containing

white counters and black counters.

There are 20 counters in the bag altogether.

The probability of choosing a

white counter from the bag is 0.75

(a) How many white counters are in the bag?

(b) Megan adds more black counters to the bag.

How many black counters must she add so that the probability of

choosing a white counter is 0.25?

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Answer 1

(a) 15

(b) 40

Explanation:

(a) There are 20 counters, and the probability of selecting a white counter is 0.75.

0.75 = x / 20

x = 15

(b) The probability changes to 0.25. The number of black counters that must be added is:

0.25 = 15 / (20 + x)

20 + x = 60

x = 40