Question 1:   How many miles are there in 21.0 km ? 


Answer 1:

From Appendix D, we know that 1 mile is equivalent to 1.609 km.


The ratio of                              is called a conversion factor .


It has a value of unity.  And we know, if we multiply any quantity by one, the value of this quantity will not change. Thus 21.0 km is equivalent to