Which of the following is linear equation.

The average of a,b,c is 20 and that of b,c,d is 25, if d=30, then the value of a is-

What is the sum of first 14 natural numbers?

A man invested a certain sum in scheme A at 15% p.a. for 2 years and earned Rs 1950 as simple interest. He increased his sum by Rs. ‘x’ and invested in another scheme B at 10% p.a. C.I. for 2 years and received Rs. 1680 as compound interest. Find the value of ‘x’. 

ABC is an isosceles triangle with AB = AC. The side BA is produced to D such that AB = AD. If ∠ABC = 30°, then ∠BCD is equal to 

One angle of a triangle is 55°. If the other two angles are in the ratio 9:16, find the angles?

Sanjana invested Rs. 15000 in SI at the rate of 2x% per annum for two years and the same amount is invested in CI at the same rate of interest if she received Rs.150 more interest than S.I, then find the rate of interest per annum?

Directions: The following questions are accompanied by three statements (A) or (I), (B) or (II), and (C) or (III). You have to determine which statement(s) is/are sufficient/necessary to answer the questions.

What is the non-voting population of a certain country?
A. Only males above 21 years of age can vote.
B. Males above 21 years form 30% of the total population.
C. The total population of the country is 30 million.