When you place resistances in series, their ohmic values add together to get the total resistance. This is easy to imagine, and it’s easy to remember!
Suppose resistors with the following values are connected in series, as shown in following figure 112 Ω, 470 Ω, and 680 Ω. What is the total resistance of the series combination?
Simply add up the values, getting a total of 112 + 470 + 680 = 1262 Ω. You might round this off to 1260 Ω. It depends on the tolerances of the resistors—how precise their actual values are to the ones specified by the manufacturer.
Three resistors in series. Illustration for mentioned problem . Resistance values are in ohms.