Question

Sum of how many terms of the arithmetic progression 3,7,11.....is 300?

Answer 1

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Answer 2

Answer:

Step-by-step explanation:

3, 7, 11, .....

Sn = 300

n = ?

a = 3

d = 7 - 3 = 4

Sn = 300

n/2 [ 2a + (n - 1) d ] = 300

n [ 2(3) + (n - 1) 4 ] = 600        

n [ 6 + 4n - 4 ] = 600

6n + 4n² - 4n = 600

4n² + 2n - 600 = 0

2n² + n - 300 = 0       ( ÷ by 2)

( 2n + 25) ( 2n - 24) = 0

n = 12               ( n can't be negative)