# Choose the correct answer in each of the following questions:

Question:

Choose the correct answer in each of the following questions:

If $a_{n}$ denotes the $n$th term of the AP $3,8,13,18, \ldots$ then what is the value of $\left(a_{30}-a_{20}\right) ?$

(a) 40

(b) 36

(c) 50

(d) 56

Solution:

The given AP is 3, 8, 13, 18, ... .

Here, a = 3 and d = 8 − 3 = 5

$\therefore a_{30}-a_{20}$

$=[3+(30-1) \times 5]-[3+(20-1) \times 5] \quad\left[a_{n}=a+(n-1) d\right]$

$=148-98$

$=50$

Thus, the required value is 50.

Hence, the correct answer is option C.