TalentJR apps
A fast calculator also checks fast. Add the digits of a number again and again until one digit is left — its nine-check number. Do the same sum with the nine-check numbers. If the result does not match the nine-check number of the answer, the answer is wrong.
✓ You passed this lesson’s test.
Casting out nines — “shrink every number to one digit and do the same sum with those”
Use it for: Checking long multiplication and addition in exams, olympiad answers and homework before you hand it in.
Check: 38 × 23 = 874, not 864 ✓
Work it out in your head or on paper, type the answer and press Check. Stuck? Press “Show me how”.
Right: 0 · Tried: 0
20 questions. Check each answer, then go to the next one. Get 16 or more right to pass — and beat the clock: finish within 4 min.
🏅 Sign in with Google to earn the 🔍 Nine Detective badge when you pass — and a certificate when you finish all 5 lessons of Part 3 · Speed dividing, percentages and checking. You can still take the test without signing in.
Why does it work? When should you use it? Ask in English, मराठी or हिंदी.
Sign in with Google to ask Free — 20 questions a day.
Prefer a real teacher? TalentJR teachers take live online classes anywhere in India and visit homes in selected cities. Tell us what you need and our team will call you with timings and fees.