The number of number - pairs lying between 40 and 100 with their H.C.F. as 15 is : Choose the correct option.
A) 3  B) 4  C) 5  D) 6  E) 7
Explanation:   Numbers with H.C.F.15 must contain 15 as a factor.   Now, multiples of 15 between 40 and 100 are 45, 60, 75 and 90.   âˆ´   Number pairs with H.C.F. 15 are (45, 60), (45, 75), (60, 75) and (75, 90).   [   âˆ´   H.C.F. of (60, 00) is 30 and that Of (45, 90) is 45]   Clearly, there are 4 such pairs.   ANSWER IS 4
<result>B</result>
The number of number - pairs lying between 40 and 100 with their H.C.F. as 15 is :