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.

Number of dimes = 7. Number of quarters = 3. Total number of coins = 10. The probability that the first coin is a dime is the number of dimes divided by the total number of coins = 7 / 10. The probability that the second coin is a dime is the remaining number of dimes divided by the total number of remaining coins = 6 / 9 = 2 / 3. Probability that both coins were dimes = 7 / 10 x 2 / 3 = 14 / 30 = 7 / 15.