You needto find the distancebetweenthe two housesin the map.The scaleshowsa sampledistance.
Use the scaleto estimatethe distance.You will find that approximatelythreesegmentsthe lengthof the
scalefit betweenthe two points.Be careful—threeis not the answerto this problem!As the scaleshows
one unit equalto two miles,you mustmultiplythreeunitsby two miles.
The distancebetweenthe housesis aboutsix miles.
You can also use estimationto identifymeasurementsin othergeometricfigures.Rememberto include
wordslikeapproximately, about,orestimationwheneveryou are findingan estimatedanswer.
RulerPostulate
You haveprobablybeenusingrulersto measuredistancesfor a long time and you knowthat a ruler is a
tool with measurementmarkings.
RulerPostulate:If you use a ruler to find the distancebetweentwo points,the distancewill be the absolute
valueof the differencebetweenthe numbersshownon the ruler.
The ruler postulateimpliesthat you do not needto start measuringat the zero mark,as long as you use
subtractionto find the distance.Note,we say “absolutevalue”here sincedistancesin geometrymustalways
be positive,and subtractioncan yield a negativeresult.
Example 2
Whatdistanceis markedon the ruler in the diagrambelow?The way to use the ruler is to find the absolutevalueof differencebetweenthe numbersshown.The line
segmentspansfrom 3 cm to 8 cm.
The absolutevalueof the differencebetweenthe two numbersshownon the ruleris 5 cm. So, the line
segmentis 5 cm long.
Example 3