Question

A textbook store sold a combined total of 480 history and math textbooks in a week. The number of history textbooks sold was two times the number of math textbooks sold. How many textbooks of each type were sold?

Answer 1

h + m = 480
h = 2m

2m + m = 480
3m = 480
m = 480/3
m = 160 <=== there were 160 math books

h = 2m
h = 2(160)
h = 320 <=== there were 320 history books

Answer 2

let h = history books, and m = math books

h + m = 480

h = 2m

plug in 2m for h

2m + m = 480

3m = 480

m = 480/3

m = 160

Plug in 160 for m in one of the equations

h + m = 480

h + 160 = 480

h = 480 - 160

h = 320

h = 320, m = 160

hope this helps