Video narration
You're looking at 35 squared. The usual route is 35 times 35, a full multiplication-more work than this needs. Here's the shortcut: the final 5 guarantees the answer ends in 25. Leave those last two places settled; focus on the part before the 5. For 35, that's 3. Multiply it by the next whole number, 4: three times four is 12. Put 25 after 12; don't add it. The answer is 1,225. Use this for any positive whole number ending in 5: take the digits before the 5 as one number, multiply by the next number, and put 25 in the final two places. In place-value terms, the number is ten times that part plus five; its square is one hundred times the part times the next number, with 25 at the end. For 35 squared, multiply 3 by 4, then put 25 after it: 1,225.