Question

The number of number pairslying between 40 and 100 withtheir hcf as 15 is

Answer 1

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. Number pairs with H.C.F. 15 are (45, 60), (45, 75), (60, 75) and (75, 90).