Answer :-
a) = Let cement, sand and stone in the concrete be x, 2x and 3x,
Each bag of dry concrete is 30 kg,
so,
x + 2x + 3x = 30
or, 6x = 30
so, x = 5
Now,
one bag contaings 2×5 = 10 kg of sand.
He buys just enough sand,stone and cement to make 50 bags of dry concrete,
1 bag = 10 kg sand
50 bags = 10 × 50 kg sand = 500 kg of sand
So,
He buys 500 kg of sand.
b) =
1 bag contains
5 kg of cement, 2×5 = 10 kg of sand and 3×5 = 15 kg of stone,
so,
25 kg of cement = 5.50 euro
5 × 50 kg of cement = 5.50/25 × 250 euro = 55 euro
20 kg of sand = 2 euro
500 kg of sand = 2/20 × 500 euro = 50 euro
15 kg of stone = 3.9 euro
15 × 50 kg = 3.9/15 × 750 euro = 195 euro
Total for 50 bags, he spent 50 + 195 + 55 euro = 300 euro.
He sold it for 396 euro.
His profit percent = (396 - 300)/300 × 100%
So, His profit percent = 32%.