We bought a total of 80 books at the store. Math books cost $4 and history books cost $5. The total price was $390. How many math books did we buy?
Choose the correct choice:	A) 10	B) 20	C) 30	D) 40	E) 50
M + H = 80   H = 80 - M   4M + 5H = 390   4M + 5*(80 - M) = 390   M = 10   The answer is 10.
<result>A</result>
We bought a total of 80 books at the store. Math books cost $4 and history books cost $5. The total price was $390. How many math books did we buy?