How many odd numbers between 10 and 1,000

Hi Vincen,

You'll see some questions on the GMAT that are "just about the math." However, you might not need to do lots of math to come up with the correct answer.

Here, we're asked for the number of numbers, between 10 and 1000 that are the squares of integers. From the answers, we know that there are at least 12, but no more than 16 numbers that fit this description. Since we're given a range to work with, my though is that I should try to find the smallest and largest values, then I can just count up the number in between.

Starting at the lower end of the range, we know that….
3^2 = 9
5^2 = 25

So the smallest number is 5

Now, the upper end of the range will take a bit more work to figure out…
30^2 = 900 (we're not allowed to use even numbers though, so this calculation was just to help us "zero in" on the upper limit.
31^2 = 961 (you'll need to be comfortable doing this math by hand)

With a lower limit of 5 and an upper limit of 31, we just need to total up the ODD numbers in this range:
5 7 9
11 13 15 17 19
21 23 25 27 29
31

Total = 14

Final Answer: C

GMAT assassins aren't born, they're made,
Rich