Question

The sum of the first 20 terms of an AP whose first term and third term are 25 and 35, respectively is​

Answer 1

Answer:

Answer is 1450

Step-by-step explanation:

a = 25, a + 2d = 35 means d = 5.

The 20th term would be a + 19d = 25 + 95 = 120.

The sum of the series would be given by: [20/2] × [25 + 120] = 1450

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Answer 2

The sum of the first 20 terms of an AP whose first term and third term are 25 and 35, respectively is​

Given:

• The sum of the first $20$ terms of an AP.
• The first term is $25$.
• The third term is $35$.

Calculation:

$a=25\\a+2d=35\\25+2d=35\\2d=35-25\\2d=10\\d=10/2\\d=5$

• The $20th$ term would be

$=a+19d\\=25+19(5)\\=25+95\\=120$

• The sum of the series would be given by

$=[20/2]*[25+120]\\=10*145\\=1450$