Question

Walter has 124 bills consisting of 5 dollar bills and 10 dollar bills. If his total amount of money is $840, how many bills of each does he have?

Answer 1

For this question here are the formulas,
Let T be the number of 10's
Let F be the number 5's

Let us find the 10's first by this formula.
5(124 - T) + 10T = 840
620-5T + 10T = 840
then
5T = 220
5 5

T=44
Now let's find the F using this formula.

5F + 10T = 840
Sustitute T
5F + 10(44) = 840
5F = 400
5 5
F = 80

to Check
F + T = 124
80 + 44 = 124