The sum of first 11 terms of an A.P is 429 and the sum of next 11 terms is 1276. Find the 25th term
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Answer: Sn=n/2[2a+(n-1)d]
S11=5.5[2a+(n-1)d]
429=5.5[2a+10d]
78=2a+10d...i
Sum of the next 11terms is given by : S22-S11= 11[2a+21d]-5.5[2a+10d]
1276=11a+176d
From i). a+5d=39
>a=39-5d
>1276=11(39-5d)+176d
>1276=429-55d+176d
>1276-429=121d
847=121d
d=847/121
d=7
a=39-5(7)
a=4
Tn=4+(n-1)(7)
Tn=4+7n-7
Tn=7n-3
T25=7(25)-3
T25=175-3
T25=172
Step-by-step explanation:
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