(Average times the total number of addends) minus the given sum of the addends.
Uriel.
29
The missing addend is 1.
Sum
correct.
addend+addend=sum
missing addend
29
The missing addend is 1.
you have to count up all of the addends
248
Sum
Addend + Addend=Sum
Addend
Both are called addend
Addend Addend Sum
Addend plus addend equals sum
Identity property