Question

S= 2+4+6+.......+200

Answer 1

S=2+4+6+...+200
S=2(1+2+3+..+100)
S=2*100*101/2
S=100*101⇒S=10100

Answer 2

$\displaystyle 2+4+6+...+200=2(1+2+3+...+100)= \\ \\ =2 \times \frac{100(100+1)}{2} =2 \times \frac{100 \times 101}{2} =\not2 \times \frac{10100}{\not2} =10100$