Aptitude - Numbers - Discussion

Discussion Forum : Numbers - General Questions (Q.No. 87)

Numbers

87.

The sum of how many terms of the series 6 + 12 + 18 + 24 + ... is 1800 ?

Answer: Option

Explanation:

This is an A.P. in which a = 6, d = 6 and S_n = 1800

Then,	n	[2a + (n - 1)d] = 1800
	2

	n	[2 x 6 + (n - 1) x 6] = 1800
	2

3n (n + 1) = 1800

n(n + 1) = 600

n² + n - 600 = 0

n² + 25n - 24n - 600 = 0

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

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

n = 24

Number of terms = 24.

Discussion:

15 comments Page 2 of 2.

Vetri said: 8 years ago

Please explain me 3rd step.

How you get 3n(n+1)=1800?

(1)

Dipu samanta said: 3 years ago

Why let 25n and 24n? Please explain me.

(1)

Biswajit borah said: 3 years ago

Please explain, How come 25 and 24?

(1)

Lahari said: 7 years ago

Please explain me the 3rd step.

(1)

Suyog said: 9 years ago

Nice move @Albin.

(1)

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