Question

the difference of the sum of even numbers and sum of odd numbersbetween 10 and 2o is

Answer 1

Sum of 5 even numbers 11-20 = $12+14+16...$
First digits' sum = $2+4+6...$

Sum of 5 odd numbers between 10-20 = $11+13+15...$
First digits' sum = $1+3+5...$

Notice that each of the numbers in the one's place of the even numbers has a greater numerical value than that of the odd numbers.

To show the relation - $(1+1)+(3+1)+(5+1)=2+4+6$
There are 6 odd and even numbers altogether. 
So, difference (one's place) is - $1*6=6$

Now, what

Answer 2

sum of even numbers is 12+14+16+18=60
sum of odd numbers is 11+13+15+17+19=70
70-60=10