A cement mixture costs $33 a ton. It is composed of Grade A cement at $36 a ton and Grade B cement at $24 a ton. How were these two cements mixed?

If we used “a” tons of grade A and “b” tons of grade B we would get a + b tons of mixture.
Converting to costs we get 36a + 24b = 33(a + b)
36a + 24b = 33a + 33b
36a - 33a = 33b - 24b
3a = 9b
a = 3b
This means the mixture contains 3 times as much of grade A than grade B
The ratio of grade A : grade B = 3 : 1

For example if we mixed 3 tons of A with 1 ton of B we would get 4 tons of mixture
The cost would be 3 x 36 + 1 x 24 = 108 + 24 = $132 for 4 tons = $33 per ton