The sum of the first 8 terms of an arithmetic sequence is 136 and the sum of the first 12 terms is 300. a) What is the sum of the first and the 8th terms? b) What is the sum of the first and the 12th terms ? c) What is the number got by adding three times the first term to the 19th term ?
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Step-by-step explanation:
Correct option is B) 154
Sum of first n th
term of an AP=S
n = 2n
[2a+(n−1)d]
Where n= no.of tern=8
d= common difference between each term=3.5
a= first term=7
∴S 8= 28 [2×7+(8−1)3.5]
⇒S 8 = 28 [14+7×3.5]
⇒S 8 =4[14+24.5]
⇒S 8 =4×38.5
⇒S 8
=154.0
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