Question

Anyone here to solve it

Answer 1

Let the number of books purchased for ₹ 800 be x

Then , cost of each book= ₹ 800/x……..(1)

If he buys 4 more books, then number of books= x+4

Cost of each book= ₹ 800/(x+4)..........(2)

A.T.Q

800/x - 800/(x+4)= 10

(800x+ 3200-800x)/x(x+4)= 10

3200= 10x(x+4)

3200= 10x²+40x

10x²+40x=3200

10x²+40x-3200=0

10( x²+4x-320)=0

x²+4x-320=0

x²+20x-16x-320=0

x(x+20)-16(x+20)=0

(x+20) (x-16)=0

x+20=0   or   x-16=0

x= -20    or    x= 16

[Numbers of books cannot be negative]

Neglecting x=-20, we get x=16

Hence, number of books purchased =16

Answer 2

hi Vanshika ,

Let number of books = x
Let cost of each book = y

so given
xy = 800 ...(1)
(x+4)(y-10) = 800 ...(2)

from (2)
xy - 10x + 4y - 40 = 800 

using (1) xy = 800
800 - 10x + 4y - 40 = 800
4y = 10x + 40

from (1)
y = 800/x

so
x(800/x) = 10x + 40
800 = 10x + 40
10x = 760
x = 76

Hence answer is he bought 76 books

Hope it helped
Let me know if any doubts
Cheers !!!