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The first term of an A.P. is 5, the common difference is 3, and the last term is 80; find the number of terms.
The first term of an A.P. is 5, the common difference is 3, and the last term is 80; find the number of terms.
Arithmetic Progressions | CBSE | Class 11 | Exercise 19.2 | Maths | RD Sharma
The first term of an A.P. is 5, the common difference is 3, and the last term is 80; find the number of terms.

Answer:

Given,

First term, a = 5; last term, l = an = 80

Common difference, d = 3

an = a + (n – 1) d

an = 5 + (n – 1)3

= 5 + 3n – 3

= 3n + 2

Put an = 80 as 80 is last term of A.P.

3n + 2 = 80

3n = 80 – 2

3n = 78

n = 78/3

= 26

Total 26 terms exists in the A.P.

i

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