Question

Assertion : Sum of first 10 terma of the arithmetio progreasion $-0.5,-1.0,-1.5,\dots \dots \dots$ is 31 .
Reason : Sum of $n$ terma of an AP is given aa $S_n=\frac{n}{2}[2a+(n-1\left)d\right]$ where $a$ is firat term and $d$ common difference.

• A. (d) Assertion (A) is false but reason (R) is true.
• B. (c) Asaertion (A) is true but reason (R) is false.
  
• C. (b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
  
• D. (a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
  

Answer 1

The correct option is A (d) Assertion (A) is false but reason (R) is true.

Aasertion, $S_{10}$ $=\frac{10}{2}\left[2\right(-0.5)+(10-1\left)\right(-0.5\left)\right]$
$=5[-1-4.5]$
$=5(-5.5)=27.5$
Assertion (A) is false but reason (R) is true.
Thus (d) is correct option.