The graph shows the temperature of water in a pot from 1900 to 19 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 1925 to 1930? Give your answer in °C/min.

(a)
Temperature of water that reached 60°C at 19 10.

From 19 10 to 19 30: 20 min

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

(b)
Decrease in temperature of water
From 19 00 to 19 05: 82°C - 76°C = 6°C
From 19 5 to 19 10: 76°C - 60°C = 16°C
From 19 10 to 19 15: 60°C - 45°C = 15°C 
From 19 15 to 19 20: 45°C - 37°C = 8°C 
From 19 20 to 19 25: 37°C - 32°C = 5°C
From 19 25 to 19 30: 32°C - 24°C = 8°C

Two 5-minute intervals that the temperature of water decreases at the same rate are 19 15 to 19 20 and 19 25 to 19 20.

(c)
Change in temperature per minute from 19 25 to 19 30
= 5 ÷ 5
= 1°C/min

Answer(s): (a) 20 min; (b) 19 15 to 19 20, 19 15 to 19 20; (c) 1°C/min