Average temperature during the first three days and the last three days of a week is 58° and 42° respectively. If the ratio of the average temperature of the whole week to the temperature on the fourth day is 4 : 3, find the temperature on the fourth day.

ATQ, Average temperature of the first three days = 58°. Total temperature of the first three days = 58 × 3 = 174°. Average temperature of the last three days = 42°. Total temperature of the last three days = 42 × 3 = 126°. Let the temperature on the fourth day be x°. Total temperature of the whole week = 174 + 126 + x = 300 + x. Average temperature of the whole week = (300 + x)/7. Given ratio: Average temperature of week : Fourth day temperature = 4 : 3 So, (300 + x)/7 : x = 4 : 3 3(300 + x) = 4 × 7x 900 + 3x = 28x 28x − 3x = 900 25x = 900 x = 900/25 x = 36 Therefore, the temperature on the fourth day is 36°.