Just confused!

[email protected] wrote:How many odd integers between 200 and 600 are there such that their tens digit is even?

A. 20
B. 25
C. 100
D. 150
E. 200

Take the task of "building" suitable numbers and break it into stages.

Stage 1: Select a hundreds digit
The hundreds digit must be 2, 3, 4 or 5, so we can complete stage 1 in 4 ways

Stage 2: Select a tens digit
The tens digit must be 0, 2, 4, 6 or 8, so we can complete stage 2 in 5 ways

Stage 3: Select a units digit
The units digit must be 1, 3, 5, 7, or 9, so we can complete stage 3 in 5 ways

By the Fundamental Counting Principle (FCP), we can complete all 3 stages (and thus build a suitable number) in (4)(5)(5) ways ([spoiler]= 100 ways[/spoiler])

Answer: C

Cheers,
Brent

Aside: For more information about the FCP, watch our free video: https://www.gmatprepnow.com/module/gmat-counting?id=775