Question

The first and last terms of an A.P. are 1 and 11. If the sum of its terms is 36, then the number of terms will be
(a) 5
(b) 6
(c) 7
(d) 8

Answer 1

Answer:

The number of terms will be 6 .

Among the given options option (b) is correct.

Step-by-step explanation:

Given :  

first term , a1 = 1, last term , an = l  = 11 = l , Sn = 36

By using the formula ,Sum of nth terms , Sn = n/2 [a + l]

Sn = n/2 [1 + 11]

36 = n/2 × (12)

36 = 6n

n = 36/6

n = 6

Hence, the number of terms will be 6 .

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Answer 2

Answer : Numbers of terms = 6

EXPLANATION:

Given,

The first term of an AP = a = 1

The last term of an AP = an = 11

Sum of the terms = 36

We know that,

Sum of terms in an AP = n/2 [a + an]

36 = n/2 [a + an]

36 = n/2 [1 + 11]

36 = n/2 [12]

=> 36 = 6n

=> n = 36/6

=> n = 6

Therefore, there are 6 terms in the AP.