The graph shows the temperature of water in a pot from 2200 to 22 30.

1. For how many minutes was the temperature of the water 60°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 2225 to 2230? Give your answer in °C/min.

(a)
Temperature of water that reached 60°C at 22 10.

From 22 10 to 22 30: 20 min

Duration that the temperature of water that reached 60°C and below = 20 min

(b)
Decrease in temperature of water
From 22 00 to 22 05: 85°C - 72°C = 13°C
From 22 5 to 22 10: 72°C - 60°C = 12°C
From 22 10 to 22 15: 60°C - 52°C = 8°C 
From 22 15 to 22 20: 52°C - 35°C = 17°C 
From 22 20 to 22 25: 35°C - 28°C = 7°C
From 22 25 to 22 30: 28°C - 11°C = 17°C

Two 5-minute intervals that the temperature of water decreases at the same rate are 22 15 to 22 20 and 22 25 to 22 20.

(c)
Change in temperature per minute from 22 25 to 22 30
= 10 ÷ 5
= 2°C/min

Answer(s): (a) 20 min; (b) 22 15 to 22 20, 22 15 to 22 20; (c) 2°C/min