Is there a trick to finding the number of odd numbers b/w two values?

You can use the exact formula. What is number of odd numbers between $11$ and $30$?

$$n = (29-13)/2 + 1 = 16/2 + 1 = 9$$

Let's list them out to make sure $: 13, 15, 17, 19, 21, 23, 25, 27, 29.$ There are $9$ of them, so that is correct. By the way, your formula was calculated wrong. $$n = (28-12)/2 + 1 = 16/2 + 1 = 8 + 1 = 9 (12, 14,16,18,20,22,24,26,28)$$

Method 1:

If you can find the number of numbers, and you can find the number of even numbers, ....

Method 2:

The number of odd numbers between 11 and 30 is the same as the number of even numbers between 12 and 31.