| 17. | What will be the least number which when doubled will be exactly divisible by 12, 18, 21 and 30 ? | |||||||
Answer: Option B Explanation:
L.C.M. of 12, 18, 21 30 2 | 12 - 18 - 21 - 30
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= 2 x 3 x 2 x 3 x 7 x 5 = 1260. 3 | 6 - 9 - 21 - 15
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Required number = (1260 รท 2) | 2 - 3 - 7 - 5
= 630.
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| 18. | The ratio of two numbers is 3 : 4 and their H.C.F. is 4. Their L.C.M. is: | |||||||
Answer: Option D Explanation:
Let the numbers be 3x and 4x. Then, their H.C.F. = x. So, x = 4. So, the numbers 12 and 16. L.C.M. of 12 and 16 = 48. |
| 19. | The smallest number which when diminished by 7, is divisible 12, 16, 18, 21 and 28 is: | |||||||
Answer: Option B Explanation:
Required number = (L.C.M. of 12,16, 18, 21, 28) + 7
= 1008 + 7 = 1015 |
| 20. | 252 can be expressed as a product of primes as: | |||||||
Answer: Option A Explanation: Clearly, 252 = 2 x 2 x 3 x 3 x 7. |