The key concept here is setting up a counting equation and isolating the unknown variable — this is a classic Word Problem / Algebraic Expression question on the GMAT Focus.
The common trap: students try to solve for the number of ministers who brought 3 assistants directly without first building the total-count equation. Instead, work backwards from x.
Let k = number of finance ministers who brought 3 assistants (this is what we want).
Then (18 − k) ministers brought 2 assistants.
Step 1 — Count every group at the summit:
• Finance ministers: 18
• Spouses: y ministers came WITHOUT a spouse, so (18 − y) brought a spouse → (18 − y) spouses
• Assistants: k ministers brought 3 each, and (18 − k) brought 2 each → 3k + 2(18 − k) = 3k + 36 − 2k = k + 36
• Journalists: 24
Step 2 — Write the total equation:
x = 18 + (18 − y) + (k + 36) + 24
x = 18 + 18 − y + k + 36 + 24
x = 96 − y + k
Step 3 — Solve for k:
k = x − 96 + y
The answer is A.
Common trap: Some students forget that the y ministers who came WITHOUT a spouse still count as ministers — so the minister count stays 18, but the spouse count drops by y. Keep those two groups separate in your accounting.
Takeaway: In "how many in terms of x and y" problems, always build your total expression first, then isolate the target variable by moving everything else to the other side.