1.  Which of the following is a pair of co- primes?

16,62
18,25
21,35
23,92

```Answer

Answer: Option  B Explanation:H.C.F. of 18 and 25 is 1.
So, they are co-primes. ```

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2.  Which of the following has most number of divisors?

99
101
176
182

```Answer

Answer: Option  C Explanation:99 = 1*3*3*11;  101= 1*101
176 = 1*2*2*2*2*11;       182 = 1*2*7*13
So, divisors of 99 are 1,3,9,11,33 and 99;
divisor of 101 are 1 and 101;
divisor of  176 are 1,2,4,8,16,22,44,88 and 176;
divisors of 182 are 1,2,7,13,14,26,91 and 182.
Hence, 176 has the most number of divisors. ```

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3.  Three numbers which are co - prime to each other are such that the product of the first two is 551 and that of the last two is 1073. The sum of the three numbers is?

75
81
85
89

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Answer: Option  C Explanation:Since the numbers are co - prime, they contain only 1 as the common factor.
Also, the given two products have the middle number in common.
So, middle number = H.C.F. of 551 and 1073 = 29;
First number = (551/29) = 19; Third number = (1073/29) = 37.
Therefore required sum = (19 + 29 + 37) = 85. ```

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4.  Three numbers are in the ratio of 3:4:5 and their L.C.M. is 2400. Their H.C.F is?

40
80
120
200

```Answer

Answer: Option  A Explanation:Let numbers be 3x, 4x and 5x. Then, their L.C.M = 60x
So, 60x =2400 or x = 40.
Therefore the numbers are (3*40). (4*40) and (5*40).
Hence required H.C.F. = 40. ```

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5.  Three numbers are in the ratio 1:2:3 and their H.C.F. is 12. The numbers are?

4,8,12
5,10,15
10,20,30
12,24,36

```Answer

Answer: Option  D Explanation:Let the required number be x, 2x an 3x. Then, their H.C.F. = x. so, x = 12.
Therefore the numbers are 12,24 and 36. ```

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