The average temperature on Tuesday, Wednesday, and Thursday was 41 degrees, and on Wednesday, Thursday and Friday was 40 degrees. If on Friday it was exactly 39 degrees, then what was the temperature on Tuesday?

Answer: Option A

Tue + Wed + Thu = 41° × 3 = 123°.....(i)
Wed + Thu + Fri = 40° × 3 = 120° .....(ii)
(i) - (ii)
After solving both, we get
Tue - Fri = 3°
Tue = 3° + Fri
= 3° + 39°
= 42°