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The first term of an AP is 5 and the last term is 45 . If the sum of all the terms is 400 the number of terms is

Posted by Janhavi Kashyap 5 years, 8 months ago

CBSE > Class 10 > Mathematics

1 answers

Gaurav Seth 5 years, 8 months ago

In an AP,

First term (a) = 5

Last term (l) = 45

Sum of the terms of the AP (Sn) = 400

Number of terms = (n) = ?

Common difference = (d) = ?

Now,

Sn = n/2 × (a + l)

=> 400 = n/2 × (5 + 45)

=> n/2 × 50 = 400

=> n = (400 × 2)/50

=> n = 16

1Thank You

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