Problem:
2+3+526 equals
Answer Choices:
A. 2+3−5
B. 4−2−3
C. 2+3+6−5
D. 21(2+5−3)
E. 31(3+5−2)
Solution:
Note that (2+3+5)(2+3−5)= (2+3)2−5=(5+26)−5=26. Thus
2+3+526=2+3+526⋅2+3−52+3−5=2+3−5
Remark. In general, m+n+m+n2mn=m+n−m+n.