Question

simon has a quarter, dime, nickel, and penny in his pocket. He wants to buy a snack at the canteen that costs 40¢. If he pulls out one coin at a time, what is the probability that the first 3 coins that are equal to $0.40?

Answer 1

1/4

Explanation:

Q=event of pulling a quarter (25 cents)

D=event of pulling a dime (10 cents)

N=event of pulling a nickel (5 cents)

P=event of pulling a penny (1 cent)

Simon needs to pull out the penny last, so that the first three coins add up to $0.40.

We assume the coins are wrapped so it is a random choice.

For the first coin, probability of NOT pulling a penny is 3/4,

similarly, for the second coin, probability of NOT pulling a penny is 2/3,

for the third coin, probability of NOT pulling a penny is 1/2,

For all this to happen, we use the multiplication rule

P(3 coins but no penny) = (3/4*2/3*1/2) = 1/4