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
