Nazri put some nails into a box and the total mass was 4 kg. Hari put some screws into a similar box and the total mass was 10 kg. The screws were 3 times
as heavy as the nails.
(a) What was the mass of the nails?
(b) What was the mass of the box?

a). 3kg b). 1kg

Explanation:

let x be the mass of nails
let y be the mass of the box

We can write an equation base on the information:

x + y = 4kg
3x + y = 10kg (screw is 3 times heavier than nail)

We can solve this system of equation using elimination method to find x:

3x + y = 10
x + y = 4
——————
3x + y = 10
-1(x + y = 4)
——————
3x + y = 10
-x - y = -4
——————
2x = 6
x = 6/2 = 3

Now that we have x we can find y:

3x + y = 10
3(3) + y = 10
9 + y = 10
y = 1