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The purpose is to quickly establish implausibility of a result. Example: compute 91·18. Answer: 91·18 = 1538. This is obviously wrong because 18 is divisible by 9 and so must be the product 91·18. On the other hand, 1538 is not divisible by 9 since its digits sum up to 1 + 5 + 3 + 8 = 17 which is not divisible by 9. The correct answer is 1638.


The purpose is to quickly establish implausibility of a result. 


 


Example: compute 91·18.


Answer: 91·18 = 1538. This is obviously wrong because 18 is divisible by 9 and so must be the product 91·18. On the other hand, 1538 is not divisible by 9 since its digits sum up to 1 + 5 + 3 + 8 = 17 which is not divisible by 9. The correct answer is 1638.


Grade:12

1 Answers

Sourabh Singh IIT Patna
askIITians Faculty 2104 Points
9 years ago
Hii

thank you for the information but we expect questions. Keep posting questions and we will answer your questions.



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