AP ICET 2015 Paper

Question : 4 of 200

Marks: +1, -0

What is the sum of the first 20 terms of the Arithmetic Progression ?
I. The sum of the first term and 20th term of the AP is 120.
II. The common difference of the AP is 5.

if the statement I alone is sufficient to answer the question.
if the statement II alone is sufficient to answer the question.
if both the statements I and II are sufficient to answer the question but neither statement alone is sufficient.
if both the statements I and II together are not sufficient to answer the question and additional data is required.

Validate

Solution:

Given: Terms are in A.P
No. of terms, n = 20
The sum of first n terms of an A.P is given by

S_n=n/2=(\text "First term"+\text "last term")

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

where
a: first term
d: common difference
I. Given:First term + 20th term=120
20th term is the last term.

n=20

⇒S_20=20/2×120=1200

∴ Ι alone is sufficient.

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