Question

an ore contains 12% copper how many kilogram of or are required to get 69 kilogram of copper

Answer 1

Let x be the total weight of Ore

We are given x*12/100 = 69
                  so, x = 6900/12
                        x = 575 Kg

So, 575 Kg of ore is needed

Answer 2

We can sole this using unitary method
12% copper means
0.012kg copper in 1 kg of ore.
So 1 kg copper means (1000/120)kg of ore.
So 69kg copper means (1000/120)×69kg ore.
=8.33*69kg ore.
=575kg.
575kg ore is required to get 69 kg ore.

Hope it helps.