The easiest way to do this is to line up the decimals and add.
4.20
+ 7.70
0 + 0 = 0
7 + 2 = 9
4 + 7 = 11
Now your answer would look like this : 1190
Since I added a zero at the end to make it easier for me, I can take away that zero now.
Now I have 119.
But, we are not done. We have to add our decimal back into the answer. Since the decimal place is only moved over once in the addends, we only move in over once in our answer. Now we get 11.9. So, the pumpkins weighed 11.9 pounds all together.
Hope this helps!