Checking answers with digit sums
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Guṇitasamuccayaḥ: the product of the sums equals the sum of the product.
गुणितसमुच्चयः
Guṇitasamuccayaḥ
Meaning: The product of the sum equals the sum of the product
Example: Is 23 × 41 = 943?
- Digit sum of 23: 2 + 3 = 5. Of 41: 4 + 1 = 5.
- 5 × 5 = 25 → 2 + 5 = 7.
- Digit sum of 943: 9 + 4 + 3 = 16 → 1 + 6 = 7. They match ✓
Answer: Correct
Reduce each number to a single digit by adding its digits again and again (this 'beejank' is the remainder on division by 9). The digit sum of the answer must equal the digit sum of the product of the digit sums. If they differ, the answer is certainly wrong. The trainer shows this check after every answer.