Question

Basant is a poor boy. On his birthday some students of his class planned to give him a gift of Rs 480. But 8 of them could not contribute due to some reason in the last moment. So, each student contributed Rs 10 more. How many students contributed for the gift?

Answer 1

let the total no of students be x and each contribution be y
then acc to question
    x*y=480                                               ..1
also,
   (x-8)(y+10)=480  
    x*y-8y+10x-80=480
    x*y-8y+10x=560                                  ..2
from 1 and 2
we get while subtracting
      8y=10x-80
so y=10x-80/8  ⇒ y=5x-40/4                   ..3
substituting 3 in 1
    x(5x-40)/4=480
    5x²-40x=1920
⇒5x²-40x-1920
⇒x²-8x-384   (dividing by 5 on whole)
by factorisation 
⇒x²-24x+16x-384
⇒x(x-24)+16(x-24)
⇒(x+16)(x-24)
then x=-16,24
no of students cannot be in negative then x=24
hence total no of students contributed=24-8⇒16

:):):)hope this ans would help u...