The first term of two APS …

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Gaurav Seth 5 years, 5 months ago
Given The first term of two aps are equal and the ratios of their common difference is 1:2.if the 7th term of first ap and 21th term of second ap are 23 and 125 respectively. find two aps.
According to question we have
So a7 = 23
Now a + 6d = 23
Or a = 23 – 6d------------------1
Also a21 = 125
Now a + 20b = 125------------2
Or 23 – 6d + 20 b = 125 (from 1)
20 b – 6d = 102
10 b – 3d = 51
Now according to question d/b = 1/2
Now d = 1x and b = 2x (for some positive value x)
Now 10 b – 3d = 51
10(2x) – 3 (x) = 51
17 x = 51
Or x = 3
Therefore d = 3, b = 6
Put d = 3 in equation 1 we get
So a + 6(3) = 23
Or a = 23 – 18
Or a = 5
Therefore first A.P is 5,8,11-------and
Second A.P is 5,11,17-------
0Thank You