1.

Find sum of first 20 terms of an AP whose first term is 24 and common difference is minus 2

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Answer:

Solution :

Given:

Number of terms(N)=20

first term(a) = 24

common DIFFERENCE(d) =-2

we know that,

Sum of a A. P. =n/2(2A+(n-1)d)

=20/2(2*24+(20-1)(-2))

=10(48+19*(-2))

=10(48-38)

=10*10

=100

Hence,

The sum is 100


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