From 1 to 50 Numbers Multiples of 2=2,4,6,8⋯50 Sum of multiples of 2 =2+4+6+8+⋯+50 =2[1+2+3+4+⋯+25] =
2×25×(25+1)
2
{∵
n(n+1)
2
=1+2+⋯+n} =25×26=650 Multiples of 5=5,10,15,20,25,30, 35,40,45,50 But, 10, 20, 30, 40 and 50 are already taken as multiples of 2 . So, Remaining multiples of 5=5,15, 25,35,45 ∴ Sum of multiples of 5 =5+15+25+35+45=125 ∴ Required average =