Question

PLEASSE HELP W THIS PROBLEM:
Andy has some $10 bills and some $20 bills in a shoebox under his bed. He has a total of 47 bills worth a total of $610. How many $20 bills does he have?

Answer 1

a = $10 bills
b = $20 bills

a + b = 47 -->a = 47 - b
10a + 20b = 610
now sub 47 - b in for a in the 2nd equation
10(47 - b) + 20b = 610
470 - 10b + 20b = 610
-10b + 20b = 610 - 470
10b = 140
b = 14
now sub 14 in for b in either of the equations to find a
a + b = 47
a + 14 = 47
a = 47 - 14
a = 33
check...
10a + 20b = 610
10(33) + 20(14) = 610
330 + 280 = 610
610 = 610 (correct)

I know you only asked for the number of $20 bills, which is 14, but I had to finish the problem to be able to check my answer.