Question

Which term of the AP: 21, 42, 63, 84,... is 210? (A) 9^th (B) 10^th (C) 11^th (D) 12^th

Answer 1

Solution:

Given A.P : 21 , 42 , 63, ....,210

First term ( a ) = 21,

Common difference ( d ) = a2 - a1

= 42 - 21

= 21

Let nth term = 210

=> a + ( n - 1 )d = 210

=> 21 + ( n - 1 )21 = 210

Divide each term by 21 , we get

=> 1 + n - 1 = 10

=> n = 10

Therefore ,

10th term in given A.P is 210

Option ( B ) is correct.

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