1. Warm Up
Multiply. Write answers in simplest form:

2. Answers 1. 2. 1 2 2 1 2 3 1 1 1 2

3. Can you answer questions like these???
How many seconds are there in 2.5 hours?
70mph is equivalent to how many feet per second?

4. Dimensional Analysis (Factor-Label Method)
MCC9-12.N.Q.1
Why learn it?
A method for converting units.
Useful for solving complicated problems in physical science and chemistry.
What do I need to know?
given amount with units
desired units
conversion factors
how to multiply fractions

5. Steps:
Read the question.
Write the given number with its units.
If it is a rate, write it as a fraction. (ex. Write 70mph as
If it is not a fraction, make it a fraction with a denominator of 1. (ex. Write 2.5hr as
3. Identify the ending units.
4. Line up conversion factors so units cancel.
5. Use a calculator to multiply & divide. Write answer with remaining units.

6. Ex. 1 How many seconds are there in 2.5 hours?
Write 2.5 hrs as a fraction.
Units we want are seconds.
We know that 1 hr=60 min and 1 min = 60 sec so these fractions are equal to 1:
Which fraction will cancel out hrs?
Which fraction will cancel out min.?

7. 70mph is equivalent to how many feet per second?
Ex. 2
70mph is equivalent to how many feet per second?
Write 70mph as a fraction.
What we want to change miles to feet. We know 1mile=5280ft. Which fraction will get rid of miles?

8. 70mph is equivalent to how many feet per second?
Ex. 2
70mph is equivalent to how many feet per second?
What we want to change hours. We know 1hr=60min. Which fraction will get rid of hours?

9. 70mph is equivalent to how many feet per second?
Ex. 2
70mph is equivalent to how many feet per second?
What we want to change minutes. We know 1min=60sec. Which fraction will get rid of minutes?

10. 70mph is equivalent to how many feet per second?
Ex. 2
70mph is equivalent to how many feet per second?
You can enter in you calculator:

11. Ex. 3 Find the number of inches in 4.5 yards.
We know 1yd = 3 ft. Write a conversion factor to change from yd to ft.
We know 1ft = 1in. Write a conversion factor to change from ft to in.
Cancel units and do the calculations.

12. Ex. 4 Convert 47 miles to kilometers. (1 km = 0.621 miles)
Answer: 75.7km

13. Ex. 5 Convert 210 rpm to revolutions per second.
Answer: 3.5rev/s