Question

First term and common difference of an A.P. are 5 and 3 respectively. Find
S25. *

a = 5; d = 3; S25 =?
S25= n [2a + (n − 1)d]
2
S25 = 25[2 x 6+ (25 – 1). )
2
=25x
2
=​

Answer 1

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Answer 2

Answer:

$S _{25} = 1025$

Step-by-step explanation:

$a = 5, \: d = 3, \: n = 25 \\ S _{25} = \frac{n}{2} [2a + (n - 1)d] \\ S _{25} = \frac{25}{2} [2(5) + (25 - 1)3] \\ S _{25} = \frac{25}{2} [10 + (24)3] \\ S _{25} = \frac{25}{2} (10 + 72) \\ S _{25} = \frac{25}{2} \times 82 \\ S _{25} = 25 \times 41 \\ S _{25} = 1025$