Elevator Mechanic Practice Exam 2025 - Free Elevator Mechanic Practice Questions and Study Guide

The goal is to achieve a total resistance of 75 ohms using available resistors. In the case of combining resistors in parallel, the formula used to calculate the total resistance is different from that of series configurations.

When combining multiple resistors in parallel, the equivalent resistance can be calculated using the formula:

1/R_total = 1/R1 + 1/R2 + 1/R3 (... and so on).

Using three 225 ohm resistors in parallel will yield a total resistance of 75 ohms:

1/R_total = 1/225 + 1/225 + 1/225, which simplifies to 1/R_total = 3/225, leading to R_total = 225/3 = 75 ohms.

This configuration successfully replaces the blown resistor with a total resistance matching the original resistor's value.

The other options either do not achieve the desired resistance output or use resistor values that do not sum up to 75 ohms upon calculation. Thus, using three 225 ohm resistors in parallel is the correct approach to replace the blown 75 ohm resistor.