Question

The first two terms of an AP are 5 and 8. How many terms are less than 1000?​

Answer 1

Answer:

first term a=5, last term l=45 and S

n

= 400

Since, S

n

=

2

n

(a+l)

⇒400=

2

n

(5+45)

⇒400=

2

n

(50)

⇒400=n(25)

⇒n=16

Since, l=a+(n-1)d

⇒45=5+(16−1)d

⇒45−5=(15)d

⇒40=15d

⇒d=

15

40

⇒d=

3

8

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