Question

There are four numbers. Average of the
first three is 15 and that of the last three
is 17. If the last number is 18 find the first
number:​

Answer 1

Explanation:

let the numbers be x,y,z,a

(x+y+z)/3=15

x+y+z=45

(y+z+a)/3=17

y+z+a=51

y+z=51-a

y+z=51-18

y+z=33

x+y+z=45

x=45-(y+z)

x=45-33

x=12