There were 21 dollars in the cookie jar. Doris spent $6 from the cookie jar. Martha spent half as much as Doris. How much money, in dollars, was left in the cookie jar?
Thoughts? Step-by-step reasoning:
Martha spent 6 / 2 = 3 dollars. Martha and Doris spent 6 + 3 = 9 dollars. There were 21 - 9 = 12 dollars left in the cookie jar.
Thus, the answer is 12.