Tabulate the data as shown below.
time, min Temp, °C
------------- -------------
3 93.5
5 90.0
9 84.8
18 70.2
30 54.4
37 42.5
48 24.9
Graph the data to observe the trend of the data. Then use the graphic calculator to determine the regression line. You may also use the Microsoft Excel spreadsheet to obtain the result.
Parts 1) and 2)
The regression line has the equation
y = 98.019 - 1.5056x
where
x = time, minutes
y = temperature, °C
The correlation coefficient of R² = 0.999 (virtually equal to 1) means that the data fits a least square straight line perfectly.
Part 3)
The slope of the straight line is -1.5056.
It represents the decrease in temperature per minute.
Answer: The temperature decreases by about 1.5 °C every minute.
Part 4)
To attain a temperature of -7°C, the equation says that
98.019 - 1.5056x = -7
1.5056x = 98.019 + 7
x = 69.75 min = 70 min (approximately)
Answer: The solution freezes after about 70 minutes