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?
Martha spent 6/2=<T>divide(6, 2)=3.0 dollars.
Martha and Doris spent 6+3=<T>add(6, 3)=9 dollars.
There were 21-9=<T>subtract(21, 9)=12 dollars left in the cookie jar.
