Question 259801
10+50=80- _____ 
Add the 10 and 50
60 = 80 - ?
Subtract 60 from both sides
0 = 20 - ?
The missing value is 20.
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and 90-30=20+ _____ 
Subtrace the 30 from 90
60 = 20 + ?
Subtract 20 from both sides
40 = ?
40 is the missing value.