## Friday, November 2, 2012

### 25. Create a word problem that involves operations with rational numbers in decimal form. Make sure you solve your problem . Then, have a classmate solve your problem.

#### My question: On Friday, the temperature at Assiniboine Park in Winnipeg, MB, Canada, decreased by 2.3°C/h  for 4 hours. It then decreased by 1.4°C/h for 2 and a half hours.

a) What was the total decrease in temperature?
b) What was the rate of decrease in temperature?

Solution:
a) The time period can be represented by 4 and 2.5. The rates of the temperature decrease can be represented by -2.3 an -1.4.

Method 1: Calculate in Stages
You can represent the temperature decrease in the first 4 hours by:
4 x (-2.3) = -9.2

You can represent the total temperature decrease in the last 2 and a half hours by:
2.5 x 1.4 = 3.5

Add to determine the total temperature decrease.
(-9.20) + 3.50 = -5.7

The total decrease in temperature was 5.7°C.

Method 2: Evaluate One Expression
The total temperature decrease can be represented by:
4 x (-2.3) + 2.5 x 1.4

*Remember to use the order of operations*
B - brackets
E - exponents
D - division
M - multiplication
S - subtraction

4 x (-2.3) + 2.5 x 1.4
= -9.2 + 3.5
= -5.7

b) The average rate of decrease in temperature is the total decrease divided by the total  number of hours.
The total number of hours is 4 + 2.5 = 6.5

The average rate of decrease in temperature was 1.08333...