The graph shows the temperature of water in a pot from 1600 to 16 30.

1. For how many minutes was the temperature of the water 80°C and below? Give your answer in min.
2. During which two 5-minute intervals did the temperature of water decrease at the same rate? Give your answer in the following format. (Eg 01 00 to 01 15, 01 25 to 01 30)
3. What was the change in temperature per minute from 1620 to 1625? Give your answer in °C/min.

(a)
Temperature of water that reached 60°C at 16 10.

From 16 05 to 16 30: 25 min

Duration that the temperature of water that reached 80°C and below = 25 min

(b)
Decrease in temperature of water
From 16 00 to 16 05: 92°C - 80°C = 12°C
From 16 5 to 16 10: 80°C - 60°C = 20°C
From 16 10 to 16 15: 60°C - 55°C = 5°C 
From 16 15 to 16 20: 55°C - 36°C = 19°C 
From 16 20 to 16 25: 36°C - 29°C = 7°C
From 16 25 to 16 30: 29°C - 22°C = 7°C

Two 5-minute intervals that the temperature of water decreases at the same rate are 16 15 to 16 20 and 16 20 to 16 25.

(c)
Change in temperature per minute from 16 20 to 16 25
= 7 ÷ 5
= 1.4°C/min

Answer(s): (a) 25 min; (b) 16 15 to 16 20, 16 20 to 16 25; (c) 1.4°C/min