Question

Sum $1.3,-3.1,-7.5$, .... to $10$ terms.

Answer 1

The given series is $1.3,-3.1,-7.5,...$ to $10$ terms

$\therefore a=1.3$

$d=(-3.1-1.3)=-4.4$

$\therefore S_n=2a+(n-1)d$

$⟹S_{24}=(2\times 1.3)+[(10-1)\times (-4.4)]$

$=2.6-39.6$

$S_{10}=-37$