Question

John’s piggy bank contained 7 dimes and 3 quarters. He pulled out 1 coin without looking. Without replacing the first coin, John then pulled out a second coin.

What is the probability that both coins were dimes? Express your answer in simplest form.

Answer 1

We have to find the probability that both coins John pulled from the piggy bank were dimes. At start the piggy bank contained 7 dimes and 3 quarters ( 10 coins in total ). The probability that the first coin pulled out was a dime : 7 / 10 ( 7 favourable of 10 possible outcomes ). So if he pulled out a dime there left: 6 dimes and 3 quarters ( total: 9 coins ). The probability that the second coin pulled out was a dime : 6 / 9 ( 6 favourable of 9 possible outcomes ). Filnally: P = 7 / 10 * 6 / 9 = 42 / 90 = 7 / 15 = 0.467 = 46.7%. Answer: The probability is 7 / 15 or 46.7 %.