Question

What is a reasonable estimate for the sum of 4 1/8+3 2/3+5 1/2

Answer 1

A responsible estimate would be 14. 
You estimate each of the mixed numbers to the nearest whole number:
4 1/8=4 because 1/8 is less than 1/2 so the number stays the same
3 2/3=4 because 2/3 is grater than 1/2
5 1/2 =6 because 1/2 is equal to 1/2 which means you estimate up.
So 4+4+6=14

Answer 2

First, mentally add the whole numbers.
4+3+5=12
Now, look at the fractions. 1/8, 2/3, and 1/2.
2/3 is bigger than 1/2, so you can add in another whole number.
12+1=13
1/8 is tiny, and won't add a whole lot to the mix, so just leave that.
A reasonable estimate would be 13 1/8