problems on hcf and lcm
22.  Three numbers which are coprime 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:  
Answer: Option C Explanation:
Since the numbers are coprime, 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;
Required sum = (19 + 29 + 37) = 85. 
23.  Find the highest common factor of 36 and 84.  
Answer: Option C Explanation:
36 = 2^{2} x 3^{2} 84 = 2^{2} x 3 x 7 H.C.F. = 2^{2} x 3 = 12. 
24.  Which of the following fraction is the largest ?  
Answer: Option A Explanation:
L.C.M. of 8, 16, 40 and 80 = 80.

25.  The least number, which when divided by 12, 15, 20 and 54 leaves in each case a remainder of 8 is:  
Answer: Option D Explanation:
Required number = (L.C.M. of 12, 15, 20, 54) + 8 = 540 + 8 = 548. 