Question

solve ............................

Answer 1

Hope it helps you......

Answer 2

Solution :

Let a and d are first term and common

difference of an A.P.

Now ,

i ) 10 th term ( a10 ) = 31

=> a + 9d = 31 ---( 1 )

ii ) 15th term = 66

=> a + 14d = 66 -----( 2 )

Subtract ( 1 ) from ( 2 ) , we get

=> 5d = 35

=> d = 35/5

=> d = 7

Substitute d = 7 in equation ( 1 ) , we get

a + 9 × 7 = 31

=> a = 31 - 63

=> a = - 32

Therefore ,

a = -32 , d = 7 ,

a31 = a + 30d

= -32 + 30 × 7

= -32 + 210

= 178

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