Question

Let E(n) denote the sum of the even digits of n. For example, E(1243) = 2 + 4 = 6. What
is the value of E(1) + E(2) + E(3) + + E(100)?

Answer 1

Look numbers 1to 10 2+4+6+8=20,for 11to19 sum of last numbers is 2+4+6+8=20,similarly for (21to29 )to(91to99) is 20 so total is 20*10=200,now consider first number for 20to29 sum of all '2’ is 2*10,sum of 40to49 is 4*10 and so on …. So total is( 2+4+6+8)*10=200 total of both 200+200=400