Question

1+2-3+4-5+6-7+8-9+10-11+12

Answer 1

Add them all

1+2=3

3+4=7

5+6=11

7+8=15

9+10=19

11-12=23

23+19+15+11+7+3= 78

So Answer is 78

Answer 2

Answer:

$\maltese\underline{\textsf{\textbf{AnsWer :}}}\:\maltese✠$

✏ We're given a series of first 12 natural numbers

✏We need to find the, sum of this series

✏ sum of first n natural numbers=

$\frac{n \times ( n+ 1)}{2}$

Sum of these numbers =

$\frac{12 \times 13}{2} = 78$

$\footnotesize \longrightarrow\: \underline{ \boxed{\sf 1+2+3...+12 \: = \: 78}}$