Question

in A.P a=13,t15=55,d=?

Answer 1

a = 13

T15 = 55

=> T15 = a + (n-1)d

=> 55 = 13 + 14d

=> 14d = 42

=> $\fbox{d = 3}$

Answer 2

Here, a = 13, t15 = 55, d =?....

But, tn = a + ( n - 1 ) d
. . . . t15 = a + ( n - 1 ) d
. . . . 55 = 13 + ( 15 - 1 ) d
. . . . 55 = 13 + 14d
. . . . . 14d = 55 - 13
. . . . . 14d = 42
. . . . . d = 42 / 14
Therefore, d = 3
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