[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
