# 2 ratios (or rates) set equal. Means-Extremes Property: If = , then ad

```Geometry
Ratio:
Date: ____
&sect;12.4 Proportions
Comparison of 2 quantities of the same unit.
2 ratios (or rates) set equal.
Proportion:
Means-Extremes Property:
If
a
c
= , then ad = bc. (cross multiply)
b
d
extremes means
Examples:
1.
∆DEF is the image of ∆ABC under a size change with center O. If AB = 20, DE = 12,
and DF = 16.5 find AC.
2.
A toy train is 48 actual size. If the locomotive of the train is 10 8 inches long and 24
inches high, how long and how high is the actual locomotive?
1
7
1
3.
A Boeing 747 is about 70.5 meters long and has a wingspan of about 59.6 meters. The
wingspan on a model of this plane is 40 centimeters. What will be the length of the model?
4.
One law of physics states that the amount of pressure that a gas exerts is proportional
to the temperature of the gas in Kelvins (K), assuming a constant volume. If a gas exerts
16 lbs/in2 of pressure at a temperature of 298 K, how much pressure would the gas exert
at 278 K?
pressure
temperature
```