Question

the first and the last term of an ap are 4 and 81 respectively if the common difference is 7 how many terms are there in AP and what is their sum​

Answer 1

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Answer 2

Answer:

a = 4

l = 81

d = 7

l = a+ [n-1]d

81 = 4 + [n-1]*7

77 = [n-1]*7

n-1 = 11

n = 12 = no. of terms

sum = n/2 [ a + l ]

sum = 12/2 [4 + 81 ]

sum = 6 * 85

sum = 510

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