Here are the steps to solve this problem:
1) Express the ratio as a fraction: 28/56
2) Simplify the fraction by dividing the numerator and denominator by their greatest common factor (GCF) of 28: 1/2
This ratio tells us that for every 1 boy there are 2 girls. So the simplest ratio of boys to girls is 1:2.
2. What is a fraction?
Loosely speaking, a fraction is a quantity that
cannot be represented by a whole number.
Why do we need fractions?
Consider the following scenario.
Can you finish the whole cake?
If not, how many cakes did you
eat?
1 is not the answer,
neither is 0.
This suggest that we need a
new kind of number.
3. Definition:
A fraction is an ordered pair of whole numbers, the 1st one
is usually written on top of the other, such as 遜 or 他 .
a numerator
b denominator
The denominator tells us how many congruent pieces
the whole is divided into, thus this number cannot be 0.
The numerator tells us how many such pieces are
being considered.
4. Examples:
How much of a pizza do we have below?
we first need to know the size of the original pizza.
The blue circle is our whole.
- if we divide the whole into 8
congruent pieces,
- the denominator would be 8.
We can see that we have 7 of
these pieces.
Therefore the numerator is 7,
and we have
7
of a pizza.
8
5. DO NOW (not later):
Compare the number of students
sitting on left side and on the right
side of the class.
6. The number of students sitting at left side=
The number of students sitting at right side =
If we compare students sitting at left side to
students sitting at right side we get
___ students sitting at left side to _____
students sitting at right side.
7. What do we call a comparison between
two or more quantities?
We just found the
RATIO RATIO of students
sitting at left side
to right side.
Is the ratio of
students sitting at
left side to right
side the same ?
No, when writing a ratio, ORDER matters.
9. How many basketballs to footballs are
there?
For every 4 basketballs
there are 6 footballs.
The ratio is 4 to 6.
10. What are some other ways we
can write the ratio of basketball
to footballs?
Every ratio can be written in 3 ways:
4 to 6 First quantity to Second quantity Careful!!
Order matters in a ratio.
4:6 First quantity : Second quantity
4 to 6
4 First quantity divided by the second Is NOT the same as
6 quantity (as a fraction). 6 to 4
11. Equivalent Ratios
Simplify the following ratios:
4 = 4/4 =1 = 1 to 2
4 to 8 8 8/4 2
10 to 8
GCF = 4
8 to 10
Step 1 Write the ratio as a fraction
Step 2 Simplify the fraction (Find the greatest common factor (GCF) of
both numbers and divide the numerator and denominator by the GCF).
Step 3 Write the equivalent ratio in the same form as the question
12. Equivalent Ratios can be formed by
multiplying the ratio by any number.
For example, the ratio 2 : 3 can also be
written as
4 : 6 (multiply original ratio by by 2)
6 : 9 (multiply original ratio by by 3)
8 : 12 (multiply original ratio by by 4)
The ratio 2 : 3 can be expressed as
2x to 3x (multiply the original ratio
by any number x)
13. Compound Ratios
A ratio that compares more than 2 quantities
is called a compound ratio.
Example:
A cake recipe says the ratio of cups of milk, sugar,
and butter are 1:2:4.
This means that there is one cup of milk for every
two cups of sugar and four cups of butter.
14. Home assignment:
1) You go to a party where the
ratio of boys to girls is 28 to
56. Express the ratio of boys
to girls in simplest form.
2) Explain what this ratio tells
us.