1. Find the twenty fifth term of the A. P. : 12, 16, 20, 24, ..... (2 marks)
Sol. For the given A.P. 12, 16, 20, 24, .....
Here, a = t1 = 12
d = t2 – t1 = 16 – 12 = 4
We know,
tn = a + (n – 1) d
t25 = a + (25 – 1) d
t25 = 12 + 24 (4)
t25 = 12 + 96
t25 = 108
The twenty fifth term of A.P. is 108.
