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.
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 %.
