Question

Find the 20th term from the last term of the AP : 3, 8, 13, .........., 253.

• A. 100
• B. 125
• C. 148
• D. 158

Answer 1

Answer: (D)

158

First, we will find the number of terms in the sequence.
$t_n=a+(n-1)d⟹253=3+(n-1)\left(5\right)⟹253=5n-2orn=51$.
So, there are a total of 51 terms in the sequence.
The 20th term from the last is same as the 32nd term from the first.
Hence, $t_{32}=3+(32-1)\left(5\right)⟹t_{32}=3+31\left(5\right)⟹t_{32}=158.$.