Which of these combinations of resistors could make up a 50-ohm dummy load capable of safely dissipating 5 watts?

To solve this problem, you must test the combinations to find one that results in both a total resistance of exactly 50 ohms and a total power capacity of at least 5 watts. For identical resistors in parallel, total resistance is the value of one resistor divided by the number of resistors. Four 200-ohm resistors in parallel yield 50 ohms (200 / 4 = 50). Next, you must evaluate the power capacity. When identical resistors are grouped together (either in series or parallel), their power ratings add up. Four 2-watt resistors provide a total capacity of 8 watts (4 x 2 = 8). Because 8 watts easily exceeds the required 5 watts, this combination is safe and correct. Looking at the distractors, ten 1/4-watt 500-ohm resistors give 50 ohms but only provide 2.5 watts of capacity, meaning they would overheat. Two 2-watt 25-ohm resistors in series give 50 ohms but only provide 4 watts, falling short of the 5-watt requirement.