Question 1157174

Walid has 30 books some are 4 cm thick and some are 3 cm . when arranged on a library shelf they occupy 1 m . how many books of each kind does Walid  have?

let there be x books of 4cm height
and y books of 3 cm height

Total books = 30

x+y = 30---------1

Height equation
4x+3y = 100----------2

Solve 1 & 2

Multiply (1) by -4

we get -4x-4y=-120
4x+3y=100 ---(2)

Add the equations

-y =-20

y=20 Therefore x = 10