instruction:
You are given a math word problem and you are supposed to apply a single mathematical operator like addition, subtraction, multiplication, or division on the numbers embedded in the text to answer the following question and then only report the final numerical answer.
question:
i have 80 cents to buy candy . if each gumdrop costs 4 cents how many gumdrops can i buy ?
answer:
20

question:
roger went to the movies 15 times last year and 3 times this year . how many times did roger go to the movies all together ?
answer:
18

question:
a waiter had 19 customers . after some left he still had 4 customers . what 's the difference between the number of customers before leaving and after leaving ?
answer:
15