The ratio is 1:3:5
and he wants to make 180 kg
Total number of parts is 1+3+5 = 9
so 1/9 of the 180 kg has to be cement which = 1/9 * 180 = 20 kg
But he only has 15kg so he can't make 180 kg of the concrete mix.
(Though he has enough sand and gravel)
Second question
Total value of 5p coins might be = 2*5 = 10p
Total values of 10p coins might be 3*10 = 30b
So the ratio of the values is 10: 30 = 1:3 (answer)