O.M 0.N5
24. M and N represent digits in the two decimals
listed above. One of the decimals is equivalent
to 1/4 and the other is equivalent to 1/2. What
is the sum of M and N?
(A) 2
(B) 3
(C) 5
(D) 6
(E) 7

Before I answer, I should make sure you and everyone else reading knows that the current SAT (since 2016) does NOT have questions like this. The old one did, and so suspect you’re looking at older prep materials (the fact that there’s a choice E gives this away as well). Older materials aren’t completely useless—there are common threads between the old and new test, but when you’re prepping off older stuff, you’re also spending time on questions like this that you don’t need to prep for.

Now, the answer, which will be shorter than my cautions above.

The decimal equivalents of 1/2 and 1/4 are 0.5 and 0.25. Therefore, M must be 5 and N must be 2. M + N = 7.