A Pre - RMO 2015 Question

Number Theory Level 3

Let E ( n ) E(n) denote the sum of the even digits of n n . For example, E ( 1243 ) = 2 + 4 = 6 E(1243) = 2 + 4 = 6 .

What is the value of E ( 1 ) + E ( 2 ) + E ( 3 ) + ⋯ + E ( 100 ) E(1) + E(2) + E(3) + \cdots + E(100) ?


The answer is 400.

Abc Xyz by abc xyz , 18, India

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1 solution

Rishabh Jain
Dec 31, 2015

10(2+4+6+8+0){UNITS digit even} +10(2+4+6+8)+0{TENS digit even} =20*2(1+2+3+4)= 400

1 Helpful 0 Interesting 0 Brilliant 0 Confused

The times when Rishabh didn't use LaTeX for solutions :P

Mehul Arora - 4 years, 9 months ago

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