Answer: 6.93 years
Step-by-step explanation:
Given
Rate of interest is 
Future value is given by 
For the investment to double itself, i.e. 

It takes around 6.93 years to double the investment.
Speed= distance/time.
6.4/4.
1.6 meters per minute.
Answer:
400 mm
Step-by-step explanation:
8 * 10 = 80
80 * 5 = 400
400 mm
Answer:
x = ±2
Step-by-step explanation:
3x ^2 -4 = 8
Add 4 to each side
3x ^2 -4+4 = 8+4
3x^2 =12
Divide each side by 3
3x^2 =12
3x^2/3 = 12/3
x^2 = 4
Take the square root of each side
sqrt(x^2) = ±sqrt(4)
x = ±2