Question

A solution is to be kept between 77° F and 86° F. What is the range in temperature in degree Celsius (C) if the Celsius / Fahrenheit (F) conversion formula is given by F = 9/5 C + 32°?

(a) [15°, 20°]

(b) [20°, 25°]

(c) [25°, 30°]

(d) [30°, 35°]

This question was addressed to me during an online interview.

This intriguing question originated from Graphical Solution of Linear Variable in Two Variables in chapter Linear Inequalities of Mathematics – Class 11

Answer 1

Correct answer is (c) [25°, 30°]

To explain I would say: F = 9/5 C + 32°

C=(F-32°)*5/9

77° ≤ F ≤ 86°

=> 77°-32° ≤ F-32° ≤ 86° -32°

=> 45° ≤ F-32° ≤ 54°

=>45o*5/9 ≤ (F-32°) *5/9 ≤ 54°*5/9

=>25° ≤ C ≤ 30°.