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: The first number is 8

Step-by-step explanation: Let the three No. s be x, y and z respectively

given = x + y + z = 72

y=7x

z=7x-18

∴As we know x + y + z=72

i. e. x+7x+7x-18=72

15x=72+18=90

15x=90

x=90/15

∴x=8

∴y=7x

7*8=56

∴z=7x-18

56-18=38

∴The first no. is x=8

The second no. is y=7x = 56

The third no. is z=7x-18 = 38

Let the first number be x, second number be 7x and the third number be 7x-18. Then,

Sum of the numbers=72

or, x + (7x) + (7x-18) = 72

or, 15x=90

or, x=6

So, the first number is 6.