Question

In an AP,a=5,an=201 and Sn=5150.find n and d

Answer 1

a = 5

an = 201

a + (n-1)d = 201

5 + (n-1)d = 201

196 = (n-1)d --------------(1)

Now, Sn = 5150

n/2 [2a + (n-1)d] = 5150

n/2 [ 10 + (n - 1)d] = 5150

Put d = 196/(n-1) from (1)

n [ 10 + (n-1)*196/(n-1)] = 10300

n [ 206] = 10300

[n = 10300/206 = 50]

Put n = 50 in (1)

d = 196/49

[d = 4]

Thus, n = 50 and d = 4

Answer 2

Hii Friend; Thanks for asking this question.

Given:-

Sn = 5150

a = 5

an = 201

To find :-

n and d

Solution :-

We know that,

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

》 5150 = n/2 [ 5 + 201]

》5150 × 2 = 206n

》5150 × 2 / 206 = n

》 n = 50 ( Ans. 01)

Now , an = a + (n-1) d

》 201 = 5 + 49d

》 196 = 49d

》 d = 4 (Ans .02)

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