The May 2013 reprint edition shows a calculation on page 30 where current through the circuit is found by dividing the supplied voltage (5 V) by the resistor value (220 ohms). Since the components are in series, the voltage drop across the LED is not counted. True current is found by dividing the voltage drop across the resistor (2.9 V) by the resistance (220 ohms) for a current through the component of about 0.014 amperes. In a series circuit, the current is the same through all the components. I verified my calculation with an ammeter. I also verified the voltage drop across the LED is 2.1 volts. The voltage drop across the resistor plus the voltage drop across the LED equals the total supply voltage (5 volts).