1.7 Variation

w is inversely proportional to the cube of x and w is 54 when x = 3
 
 
 
 
x is jointly proportional to y and z
 
 
 
 
c varies directly as a
 
 
 
 
The electrical current, in amperes, in a circuit varies directly as the voltage.
When 15 volts are applied, the current is 5 amperes. What is the current when
18 volts are applied?
 
 
 
 
The number of aluminum cans used each year varies directly as the number of
people using the cans. If 250 people use 60,000 cans in one year, how many
cans are used each year in Dallas, which has a population of 1,008,000?
 
 
 
 
w varies inversely as x
 
 
 
 
The current in an electrical conductor varies inversely as the resistance of the
conductor. If the current is 12 ampere when the resistance is 240 ohms, what
is the current when the resistance is 540 ohms?
 
 
 
 
e varies jointly as f and g and e = 24 when f = 3 and g = 2
 
 
 
 
m is inversely proportional to n and m = 1.8 when n = 2.1
 
 
 
 
The intensity of illumination falling on a surface from a given source of light
is inversely proportional to the square of the distance from the source of light.
The unit for measuring the intensity of illumination is usually the foot candle. If
a given source of light gives an illumination of 1 foot-candle at a distance of
10 feet, what would the illumination be from the same source at a distance
of 20 feet?