Mental Math · Capstone · C1
You now have a toolkit of logical methods. The last skill is choosing the right one fast: look at the numbers, spot what makes them friendly, and reach for the move that fits. Then practise until it's automatic.
Speed drill
You get 60 seconds. Pick the right method in your head and type the answer. How many can you solve?
Adding and one number is near a ten? Round and fix. Subtracting and the numbers are close? Count up. Multiplying by 5, 9, 25, or 50? Use the shortcut. Multiplying anything else? Break it apart. Dividing? Factor the divisor or break the dividend. There is always a friendly path.
Why it works
The numbers tell you which tool to grab — look before you leap.
Best move for 68 + 19?
Spot it
19 is near 20.
Method
Round and fix: 68 + 20 − 1 = 87.
Best move for 16 × 25?
Spot it
Even × a multiple of 25.
Method
Double and halve: 8 × 50 → 4 × 100 = 400.
Best move for 504 ÷ 9?
Spot it
Digit sum 9 → divisible by 9.
Method
Break the dividend: 450÷9 + 54÷9 = 50 + 6 = 56.
Forcing one method onto every problem.
Different numbers want different moves. 19 + anything → round and fix; 16 × 25 → double and halve. Match the tool to the numbers.
Reaching for the paper algorithm under time pressure.
The mental methods are faster once they're automatic. Trust the friendly-number path.
12 problems across three tiers. Auto-graded on submit. Hints and a full walkthrough on every question. Your work is saved on this device — sign in to keep it across devices.
t₁ = 5, d = 3 and t1=5,d=3 both count. For a list of numbers, separate them with commas (e.g. 3, 10, 17).47 + 38 = ?
92 − 34 = ?
7 × 14 = ?
96 ÷ 4 = ?
297 + 58 = ?
73 − 19 = ?
48 × 5 = ?
84 ÷ 6 = ?
35² = ?
16 × 25 = ?
503 − 248 = ?
252 ÷ 9 = ?