Question

The sum of three numbers is 72

The second number is 7 times the first.
The third number is 18 less than the second.
What is the first number?

Answer 1

6

Explanation:

Let the first, second and third numbers be a, b and c respectively.

a +b +c= 72 -----(1)

b= 7a -----(2)

c= b -18 -----(3)

Substitute (2) into (3):

c= 7a -18 -----(4)

Substitute (2) and (4) into (1):

a +7a +7a -18= 72

Simplify:

15a -18= 72

Add 18 to both sides of the equation:

15a= 72 +18

15a= 90

Divide both sides by 15:

a= 90 ÷15

a= 6

Thus, the first number is 6.