You might have a flashlight that runs (2) d-cells of 1.5 volts each in series. the bulb is rated for 0.7 amps. what's its resistance?

From Ohm's law, we get the general equation that would relate the voltage, current, and resistance,

V = I x R

where V is voltage, R is resistance, and I is current. Deriving the equation for R

R = V / I

R = (1.5 volts) / (0.7 amps) = 2.14 Ohms