Question

The first and last term of an ap are 5 and 45 if the sum of all of its terms is 400 find d and n
The fourteenth term of an ap is twice the 8th term. if the 6 term is -8 then find the sum of its first 20 terms
find 6 terms from end of the ap 17 14 11 ... -40
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Answer 1

Answer:

Answer for 1st qn

Step-by-step explanation:

Given, a = 5 ; l = 45 ; Sn = 400

Sn = n /2 ( a + l)

400 = n / 2 ( 5 + 45)

800 = n ( 50)

n = 16

Sn = n/2 (2a + (n-1) d)

S(16) = 16/2 ( 2*5 + 15 d)

400 = 8 (10 + 15 d)

50 = 10 + 15 d

40 = 15 d

d = 8/3