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## Comment on

Listing and Counting## Hi Brent,

I am sorry but I am confused with the question "can be created using digits 2 and 7 only". Does that mean that the 3 digits # has to contain both 2 and 7?

Thanks a lot!

Kate

## Hi Kate,

Hi Kate,

For that question, we are basically told that the only digits we can choose from are 2's and 7's. It does not mean that every outcome must contain at least one of each digit.

For example, numbers like 222 and 777 meet the give condition.

Cheers,

Brent

## Thank you Brent, I felt like

Kate

## Hi Brent, I am confused with

How many keystrokes are needed to type numbers from 1 to 1000?

A. 2704

B. 2890

C. 2893

D. 3001

E. None of these

My approach:

For 1-9 - 9 strokes

For 10 - 99 - 90*2 strokes

For 100-999 - 999*3 strokes

For 1000 - 4 strokes

Please help me where am I wrong in this?

## The only problem with your

The only problem with your solution is the 3rd step. You have 999 integers from 100 to 999, but there are only 900 integers from 100 to 999.

Here's my full solution: https://gmatclub.com/forum/how-many-keystrokes-are-needed-to-type-number...

Cheers,

Brent

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