The sum of first four terms of the G.P. 2, 6, 18, ………, is :

1. 26

2. 80

3. 160

4. 52

The 4^th term of a G.P. is 54 and its 7^th term is 1458, the common ratio of this G.P. is :

1. $\dfrac{1}{3}$

2. 3

3. -3

4. $-\dfrac{1}{3}$

The sum of three terms (numbers) of a G.P. is $3\dfrac{1}{2}$ and their product is 1; the numbers are :

1. $\dfrac{1}{2}, 1$ and 2

2. $\dfrac{1}{3}, 3$ and 9

3. $1, \dfrac{1}{2}$ and 2

4. $2, \dfrac{1}{2}$ and 1

The sum of 20 terms of the G.P. 10, 20, 40, …… is :

1. 10(2¹⁹ - 1)

2. 10(2²¹ - 1)

3. 10(2²⁰ - 1)

4. none of these