If all the odd numbers are removed from 3 to 39, then how many numbers remain?

 the range of numbers from 3 to 39, and we need to remove all the odd numbers, leaving only the even numbers.

The even numbers between 3 and 39 form an arithmetic sequence, starting at 4 and ending at 38, with a common difference of 2. 

Formula Used: 

For AP series ,

l = a + (n -1)d 

where, l = last term, a = first term, n = no. of terms, d = common difference.

Here given that, range 3 to 39 with no odd numbers

So, numbers are 4 , 6 , 8 ............ 38.

Now, a = 4 , d = 2, l = 38 

substituting the values

38 = 4 + (n - 1)2 

38 - 4 = (n - 1)2 

n - 1 = $$\frac{34}{2}$$ 

n = 17 + 1 

n = 18 

Thus, there are 18 numbers between 3 to 39 after removing odd numbers.