TASK DEFINITION: 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.
PROBLEM: there are 28 students in mrs. riley 's class but she only has 19 pencils . how many more pencils does mrs. riley need ?

SOLUTION: 9

PROBLEM: 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 ?

SOLUTION: 15

PROBLEM: kim has 4 cousins . she wants to give each one 5 pieces of gum . how much gum will she need ?

SOLUTION:
20