Is there a trick to finding the number of odd numbers b/w two values? I know you could find the number of even numbers (since they are a multiple of two). For example the number of even numbers between $11$ and $30$ will be
$$n= \frac{28-12}{2} + 1 = 9  $$

I wanted to know is there a similar way to find the number of odd numbers b/w two extremes?
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. $$n = (28-12)/2 + 1 = 16/2 + 1 = 8 + 1 = 9 (12, 14,16,18,20,22,24,26,28)$$
The Problem What is the number of EVEN or ODD integers between two numbers n and m? 

(where m>n)

Solution:


Recall the formula (m-n+1)/2 
Calculate it. 
See below for how to interpret:


If m&amp;n are mixed signs*, you're done. That's your answer.
If m&amp;n are the same as the target**, round up.
If m&amp;n are different than the target, round down.



Details:


*mixed signs = one is even and the other is odd.
**"same as the target = if you're looking for evens, then whether m&amp;n are both even. If you're looking for odds, then whether m&amp;n are both odd.