Mathematics - Sequence & Series Question with Solution | TestHub

the difference between successive terms in progression $a$ is the opposite of the difference in progression $b$

$a_n+b_n=100$ for any $n$

$\left(a_1+b_1\right),\left(a_2+b_2\right),\left(a_3+b_3\right),\dots$ are in A.P.

${\sum }_{r=1}^{100}\left(a_r+b_r\right)=10000$