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Home » If the ratio between the sums of n terms of two arithmetic progressions is (7n + 1) : (4n + 27), find the ratio of their 11th terms.
If the ratio between the sums of n terms of two arithmetic progressions is (7n + 1) : (4n + 27), find the ratio of their 11th terms.
RS aggarwal class 11 Maths Arithmetic progressions
If the ratio between the sums of n terms of two arithmetic progressions is (7n + 1) : (4n + 27), find the ratio of their 11th terms.

Given: Ratio of sum of nth terms of 2 AP’s
To Find: Ratio of their 11th terms

Let us consider 2 AP series AP1 and AP2.
Putting n = 1, 2, 3… we get AP1 as 8, 15 22… and AP2 as 31, 35, 39….
So, a1 = 8, d1 = 7 and a2 = 31, d2 = 4
For AP1
S6 = 8 + (11 – 1)7 = 87
For AP2
S6 = 31 + (11 – 1)4 = 81
Required ratio =

8781=2927
i

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