count the number!!!

Number Theory Level 2

How many times shall the keys of a typewriter have to be pressed in order to write first 200 counting numbers,i.e.,to write 1,2,3...200?


The answer is 492.

Hritik Agarwal by hritik agarwal , 20, India

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1 solution

Efren Medallo
May 1, 2015

From 1 to 200, there are 9 one-digit numbers (1-9), 90 two-digit numbers (10-99), and 101 three-digit numbers (100-200).

Thus,

( 9 × 1 ) + ( 90 × 2 ) + ( 101 × 3 ) = 492 \large (9 \times 1) + (90 \times 2) + (101 \times 3) = 492

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