How do you know if a number is divisible by 7? - Answers

Divide the number by seven. It is divisible by seven if the result is a whole number How do you know if a number is divisible by 7.? Ans: To know the given is divisible by an number or not. Take the number which is in the units place and double it. Then by eliminating the units number, subtract the number doubled by the remaining number. Continue this process until two digits number. 1) example: Take the number 5523. The number in the units place is 3. Double that number then we get 6. Subtract it from the number leaving the units place number then it becomes 552- 6 = 546. Again double the units place number 6 that is 12. Again subtract in from the number leaving units place number that is 54-12 = 42. The 42 is divisible by 7.( 6x7=42). The the number 5523 is divisible by 7 . 2) example: Take the number 38661. Double the number in the units place 1 then it becomes 2. Subtract in from 3866 then it becomes 3864. Double the number in the units place number 4, it becomes 8. Subtract it from 386. Then it becomes 378. Double the unit place number 8 it becomes 16. Subtract it from 37. Then it becomes 21. 21 is divisible by 7. So the number 38661 is also divisible 7. 3) Example: Take the number 38662. Double the number in the units place 2, then it becomes 4. Subtract the 4 from 3866, then it becomes 3862. Double the number in the units place number 2, then it becomes 4. Subtract this 4 from 386. Then it becomes 382. Again double the number in the units place it becomes 4, Subtract it from 38 , then it becomes 36. The 36 is not divisible by 7, so the number given is also not divisible by 7. Gadde Mathew Madhukar. ( From the book " Ganitha Medhavulu and Ganitha Chitkalu by Sri S. Chandra Sekhara Sastry, Pallavi Publications, Eluru Road, Vijayawada, Andhra pradesh, India.