if sum of 3rd and4th term of gp is 60 and the sum of 6th&7th is 480 then what is the 10th term
Answer (1)
Student Expert
30th Nov, 2019
Let, a be the first term of series and r be the common ratio.
So, by question we can write-
Sum of 3rd and 4th terms-
ar^2+ar^3 = 60
Or, ar^2 (1+r) = 60 .......(1)
Sum of 6th and 7th terms-
ar^5+ar^6 = 480
Or, ar^5 (1+r) = 480 ........(2)
Now, ar^2(1+r)/60 = ar^5(1+r)/480
Or, r= ....... (solve the equation, you will get r).
Now put the value of r in eq. 1 or 2. You will get the value of a.
Now, 10th term will be-
a * r^(10-1) = ...... (solve it by putting the value of a and r)
So, by question we can write-
Sum of 3rd and 4th terms-
ar^2+ar^3 = 60
Or, ar^2 (1+r) = 60 .......(1)
Sum of 6th and 7th terms-
ar^5+ar^6 = 480
Or, ar^5 (1+r) = 480 ........(2)
Now, ar^2(1+r)/60 = ar^5(1+r)/480
Or, r= ....... (solve the equation, you will get r).
Now put the value of r in eq. 1 or 2. You will get the value of a.
Now, 10th term will be-
a * r^(10-1) = ...... (solve it by putting the value of a and r)
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