Question

what is the answer of above question ​

Answer 1

Step-by-step explanation:

this answer is helpful for your practice

Answer 2

Answer:

The correct answer to the following question will be "n=38".

Step-by-step explanation:

According to the question,

Term of AP, a=1

Last term of AP, L=aₙ=20

Sum of all the terms in AP, Sₙ=399

Now, Solution

Sum of A.P,

Sₙ=$\frac{n}{2}$(a+aₙ)

By putting the values of Sₙ, a, aₙ, we get

399=$\frac{n}{2}$(1+20)

399=$\frac{n}{2}$(21)

$\frac{399}{21}$=$\frac{n}{2}$

19=$\frac{n}{2}$

n=19×2

n=38

Learn more:

Find the sum of the AP: 2, 5,8,.....,182...

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