Change one of the $+$ signs to an equals sign so that you create an addition problem with a true answer:
$$\text{1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20}$$
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2 Answers
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Assuming the 2- is actually 20...
1+2+3+4+5+6+7+8+9+10+11+12+13+14
=
15+16+17+18+19+20
answered Feb 23, 2017 at 5:10
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3
Easy:
put '=' in between 14 and 15 ie
1+2+3+4+5+6+7+8+9+10+11+12+13+14=15+16+17+18+19+20
Easy way to find out N(N+1)/2 =
(20*21)/2 - N(N+1) /2
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$\begingroup$ You might want to look at other answers already given before adding one of your own. How does your answer materially differ from the existing one? $\endgroup$– Rubio ♦Feb 23, 2017 at 6:37
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1$\begingroup$ The other answer didn't say how it was found $\endgroup$ Feb 23, 2017 at 6:38
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$\begingroup$ @ULTIMATEGAMER07, regardless, you could have just commented with an explanation. $\endgroup$ Feb 23, 2017 at 8:23