Question

which of the A. P. 2½,4,5½,...is 31 ? Find also 10th term?

Answer 1

a10= a (n-1)d
2.5(10-1)1.5
2.5 (9)1.5
16

Answer 2

Hi ,

Given A.p is 2 1/2 , 4 , 5 1/2 ,...,31

First term ( a ) = 2 1/2 = 5/2 = 2.5

d = a2 - a1

= 4 - 2.5 = 1.5

an = 31

a + ( n - 1 )d = 31

2.5 + ( n - 1 ) ( 1.5 ) = 31

( n - 1 ) ( 1.5 ) = 31 - 2.5

n - 1 = 28.5/1.5

n - 1 = 19

n = 19 + 1

n = 20

2 )10th term = a10

= a + 9d

= 2.5 + 9 ( 1.5 )

= 2.5 + 13.5

= 16

I hope this helps you.

:)