The intensity of current varies inversely with the resistance. when the resistance is 3 ohms, the intensity of current is 9 amperes. find the resistance when the intensity of current is 18 amperes

First you need to know the equation for inverse variation. y = k/x
Next, fill in the information you know so that you can find 'k', the constant of variation.
9 = k/3 Now solving for k we get k = 27 and you have your inverse equation for this problem and can use any values for intensity or resistance.
y = 27/x or I = 27/R
18 = 27/R
18R = 27
R = 27/18
R = 1.5 ohms