Progression Practice Test 1

Question : 14 of 23

Marks: +1, -0

If the 3rd term and 7th term of AP is 20 and 48 respectively. Find the first term, common difference and its 9th term.

4, 7, 62
6, 8, 62
6, 7, 63
6, 7, 62
None of these

Solution:

Let a be the first term and r be the common difference then

t_3

= 20 ⇒ a + 2d = 20 ......(i)

t_7

= 48 ⇒ a + 6d = 48 ......(ii)
Subtracting (i) from (ii) we get
4d = 28
d = 7
Putting d = 7 in equation (i) we get
a + 2 (7) = 20
a + 14 = 20
⇒ a = 6
First term = 6 and common difference = 7
then

t_9

= a + 8d ⇒ 6 + 8 (7) = 62
Hence, 9th term = 62

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