Answer: the total number of coupon books sold is 20.
Step-by-step explanation:
Let x represent the number of coupon books that Mario sold.
Let y represent the number of coupon books that Luigi sold.
Apparently, Mario is a much better salesperson, because he sold 4 times as many coupon books as Luigi. This is expressed as
x = 4y
If Luigi sold 12 fewer coupon books than Mario, the expression would be
x = y + 12 - - - - - - - - - - -- -1
Substituting x = 4y into equation 1, it becomes
4y = y + 12
4y - y = 12
3y = 12
y = 12/3
y = 4
x = 4y = 4 × 4
x = 16
The total number of coupon books that the two boys sold is
4 + 16 = 20
