Temperatures recorded at a station during one day, in °C. 6 am 14, 9 am 19, 12 noon 27, 3 pm 30, 6 pm 22, 9 pm 17. Between which two consecutive readings was the FALL in temperature the greatest?

Take the differences of consecutive readings: +5, +8, +3, −8, −5. Only the last two are falls, and the larger of them, 8 °C, occurs between 3 pm and 6 pm. The change of 8 °C between 9 am and 12 noon is the same size but it is a rise, not a fall.