In an experiment, the temperature is 760 units at the first stage and decreases by 32 units at each next stage. At which stage will it be 280 units?

Correct answer: 16th

The governing idea is modelling repeated equal decrease as an arithmetic progression. The first-stage value is a=760, and because the temperature decreases by 32 at every step, the common difference is d=−32. The value at stage n is therefore a_n=760+(n−1)(−32). Set the target equal to 280: 760−32(n−1)=280. Hence 32(n−1)=480, so n−1=15 and n=16. Therefore the temperature is 280 units at the 16th stage, making option C correct. The negative difference must be used because the sequence decreases. Checking nearby stages gives stage 15 as 312 and stage 17 as 248, so neither neighboring option satisfies the target.