Work through the levels in order. Type your answer and press Check — open the worked solution if you get stuck. Answers like -6, 3/4 or 0.25 are typed exactly as shown. A ⭐ Bonus Challenge at the end is extra credit — skip it if the rest was hard work.
Level 1 · Warm-up
1 Work it out in your head: 297 + 48
Show worked solution
300 + 48 = 348, then take back the 3 you added: 345.
2 Add 199 to 356.
Show worked solution
356 + 200 = 556, then take back 1: 555.
3 Work it out in your head: 68 + 25
Show worked solution
68 + 2 = 70, then 70 + 23 = 93.
Level 2 · Core
4 Add these in any order you like: 4 + 97 + 6 + 3
Show worked solution
4 + 6 = 10 and 97 + 3 = 100, so the total is 110. Choosing the order makes it easy.
5 Use compensation: 458 + 99
Show worked solution
458 + 100 = 558, and you added 1 too many, so 557.
6 What is 250 + 250 + 250 + 250?
Show worked solution
Each pair makes 500, and 500 + 500 = 1000. (It is also 4 × 250.)
Level 3 · Challenge
7 Two numbers add to 500. One of them is 40 more than the other. What is the larger number?
Show worked solution
Take the 40 off: 500 − 40 = 460, so the smaller is 460 ÷ 2 = 230 and the larger is 230 + 40 = 270. (230 + 270 = 500.)
8 A number added to 275 gives 600. What is the number?
Show worked solution
Count up: 275 + 25 = 300, then 300 + 300 = 600. That is 25 + 300 = 325.
9 What is 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10?
Show worked solution
Pair them: 1 + 10, 2 + 9, 3 + 8, 4 + 7, 5 + 6 — five pairs of 11. So 5 × 11 = 55.
⭐ Bonus Challenge · only if the rest felt easy
10 Use a smart strategy: 198 + 47
Show worked solution
Jump to the friendly number: 200 + 47 = 247. You added 2 too many, so take them back: 247 − 2 = 245.