3rd grade math
posted by rodrick .
how do you tell what compatible numbers you would use and theh add example $2.75+$5.35

I never heard of "compatible numbers".
Just add them, keep the decimal point in the same place, and you get $8.10 
the answer is 8.10 you get this because if yo add.05+.05 it would =.10 so you carry the 1 to the tenths place and then add .70+.30 and then add .10 because that is the answer for the hunthenths place and then it would be.10. Then you add 2+5 then add .10 and you wouled get 8.10

Compatible numbers are numbers that are easy to compute mentally

tell what compatible numbers you would use.then add
$2.55+$1.34

 
300
+100

400
answer: 400 
What is your question Anonymous? What it looks like is that you rounded. 300+100 = 400 is correct.

Compatible 67+ 119

Tell what compatible numbers you would use then add 419+263

186