Question

Find the sum of 12th term of the following AP series 7,11 and 15.
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Answer 1

It is adding 4 each time.

Just calculate the first 12 terms and add them up.

Term 1 = 7 + 4*0 = 7
Term 2 = 7 + 4*1 = 11
Term 3 = 7 + 4*2 = 15
Term 4 = 7 + 4*3 = 19
Term 5 = 7 + 4*4 = 23
Term 6 = 7 + 4*5 = 27
Term 7 = 7 + 4*6 = 31
Term 8 = 7 + 4*7 = 35
Term 9 = 7 + 4*8 = 39
Term 10 = 7 + 4*9 = 43
Term 11 = 7 + 4*10 = 47
Term 12 = 7 + 4*11 = 51

Sum of first 12 terms = 348

Answer 2

Answer:the sum of the 12th term of the AP is 348

Explanation:

7,11,15

Common difference=d=11-7

d=4

First term=7

Using the formula

Sn=n/2 x (2a+d x (n-1))

S12=12/2 x (2x7+4x(12-1))

S12=6 x (14+4x11)

S12=6 x (14+44)

S12=6 x 58

S12=348