Sum of N Terms When First Term, Last Term and Number of Terms are Given


 
 
Concept Explanation
 

Sum of N Terms When First Term, Last Term and Number of Terms are Given

Sum of All Terms When First Term, Last Term and Number of Terms is Given: The sum can be found by using the formula.

large _{S_{n}}=frac{n}{2}(a+l)

For Example: Find the sum of an AP. whose first term is 30, the last term is 51 and the number of term is 8

 a= 30

l= 51

n= 8

_{S_{8}}=frac{8}{2}(30+51)=frac{8}{2}times 81=4times 81=324

Sample Questions
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Question : 1

If the first term the last term and the sum of all the terms of an AP a, b and c respectively the number of terms in the AP is

Right Option : A
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Explanation
Question : 2

If the last term , first term and the sum of all terms of an AP are 23, -19, and 30 respectively the number of terms in the AP is ___________

Right Option : D
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Explanation
Question : 3

If the last term,  the number of terms and the sum of all the terms of an AP are 68, 20 and 790 respectively,  its first term is ___________

Right Option : A
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Explanation
 
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