Number System
Aptitude

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Q.

How many keystrokes are needed to type numbers from 1 to 1000 on a standard keyboard?

 A.

3001

 B.

2893

 C.

2704

 D.

2890

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Solution:
Option(B) is correct

While typing numbers from 1 to 1000, you have 9 single digit numbers from 1 to 9. Each of them requires one keystroke. That is 9 key strokes.

There are 90 two-digit numbers, from 10 to 99. Each of these numbers requires 2 keystrokes. Therefore, one requires 180 keystrokes to type the 2 digit numbers.

There are 900 three-digit numbers, from 100 to 999. Each of these numbers requires 3 keystrokes. Therefore, one requires 2700 keystrokes to type these 3 digit numbers.

Then 1000 is a four-digit number which requires 4 keystrokes.

Totally, therefore, one requires $9 + 180 + 2700 + 4 =$ 2893 keystrokes.


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