Question

An inch in equal to about 2.54 centimeters. Write an expression which estimates the number of centimeters in x inches. Then estimate the number of centimeters in 12inches.

Answer 1

1 inch = 2.54 centimeters. this is a ratio. 

expression: x inches * _2.54 centimeters_ = # of centimeters in x inches
                                                 1 inch 
the reason the 1 inch is in the denominator is to cancel out the inches for x so that you are only left with centimeters. 

estimate: 12 inch * _2.54 centimeters_ =  30.48 centimeters.  
                                       1 inch