A word problem is a tiny story with numbers in it. Your job is to figure out what the story is asking and which calculation answers the question.
When the story is about combining or getting more, you usually add:
Example. The library had 482 books. 156 new books arrived. How many in total?
Plan: combine → add. 482 + 156 = 638.
When the story is about removing, comparing or finding what's left, you usually subtract:
Example. The bakery baked 540 rolls. By lunch, 287 had been sold. How many were left?
Plan: remove → subtract. 540 − 287 = 253.
"How many more X than Y?" is comparison — you subtract the smaller from the larger.
Tom has 234 stickers. Eva has 158. How many more does Tom have?
Plan: difference → subtract. 234 − 158 = 76.
Some problems hide two steps. Read carefully — a single calculation might not be enough.
Sam had €500. He spent €185 on shoes and €120 on a jacket. How much does he have left?
Step 1: total spent = 185 + 120 = 305.
Step 2: money left = 500 − 305 = 195.
After you compute, write a short sentence that answers the question. Don't leave just a bare number — the question asked for something specific (books, rolls, money…).