Question

In a given A.P., $T_{25}-T_{20}=15$. $\therefore$ $d=$............. for the A.P.

• A. $5$
• B. $3$
• C. $25$
• D. $120$

Answer 1

The correct option is B $3$

Given: $T_{25}-T_{20}=15$ ........... $\left(i\right)$

We know that, $n^{th}$ term of an A.P. is given by $T_n=a+(n-1)d$

$\therefore T_{25}=a_1+(25-1)d=a_1+24d$ and
$T_{20}=a_1+(20-1)d=a_1+19d$
Now, $T_{25}-T_{20}=a_1+24d-a_1-19d=5d$
$⟹15=5d$ ...... From $\left(i\right)$

$⟹d=3$

Hence, the answer is $3$.