Average temperature during the first three days and the last three days of a week is 52° and 36° respectively. If the ratio of the average temperature of the whole week to the temperature on the fourth day is 7 : 5, find the temperature on the fourth day.

ATQ, Average temperature of the first three days = 52°. Total temperature of the first three days = 52 × 3 = 156°. Average temperature of the last three days = 36°. Total temperature of the last three days = 36 × 3 = 108°. Let the temperature on the fourth day be x°. Total temperature of the whole week = 156 + 108 + x = 264 + x. Average temperature of the whole week = (264 + x)/7. Given ratio: Average temperature of week : Fourth day temperature = 7 : 5 So, (264 + x)/7 : x = 7 : 5 5(264 + x) = 7 × 7x 1320 + 5x = 49x 49x − 5x = 1320 44x = 1320 x = 1320/44 x = 30 Therefore, the temperature on the fourth day is 30°.