Question

Find the 17th term of an arithmetic progression. If 15th and 21st term of arithmetic progression is 30.5 and 39.5 respectively.

• A. 38
• B. 35.5
• C. 36
• D. 33.5

Answer 1

Answer:

D. 33.5

$T_{15} = a + 14d = 30.5$ ------ (1)

$T_{21} = a + 20d = 39.5$ ------ (2)

Subtract equation 1 from equation 2

$6d = 9$

$d = 1.5$

Put the value of d in equation 1

$a + 14 \times1.5 = 30.5$

$a = 30.5 - 21$

$a = 9.5$

$T_{17} = a + 16d$

$= 9.5 + 16 \times1.5$

$= 33.5$