cross reducing
TRANSCRIPT
A Shortcut
Using Cross-Division to put our multiplication answers into
simplest form quickly.
Simplifying Fractions
• Start with a multiplication statement that looks like it will need to be simplified.
2 3
3 5=ᄡ
Cross Reducing
• Normally, you would multiply the top numbers and then the top.
• Then check to see if your fraction is in simplest form.
2 3
3 5=ᄡ
2 3 6 3 2
3 5 15 3 5
ᄡ ᄌ= =
ᄡ ᄌ
Cross Simplifying
• Now let’s look to see if we can cross reduce.
• First check the upper left and lower right corner.
• Is there any number that can divide evenly into 2 or 5?
2 3
3 5=ᄡ
Nope!
Cross Simplifying
• Now let’s look to see if we can cross reduce the other pair.
• Check the upper right and lower left corners.
• Is there any number that can divide evenly into 3 or 3?
2 3
3 5=ᄡ
Yes! 3
Let’s divide
• Since we can divide three into three at the top and do the same at the bottom, we do it right in the problem.
2 3
3 5=ᄡ
Cross out• Cross out the 3’s
• Divide the bottom left number by 3.
• Replace the three with a one.
• Divide the top right number by 3.
• Replace the three with a one.
2 3
3 5=ᄡ
1
1
New Problem
• Multiply the top numbers.
• Multiply the bottom numbers.
• It will often be in simplest form after cross reducing and multiplying.
2 3
3 5=ᄡ
1
1
2 1 2
1 5 5=ᄡ
Watch one• Cross out the numbers divisible by 5.
• Divide the bottom left number by 5.
• Replace the five with a one.
• Divide the top right number by 5.
• Replace the ten with a two.
2 10
5 11=ᄡ
1
2
New Problem
• Now proceed with the newly formed problem.
2 10
5 11=ᄡ
1
2
2 2
1 11=ᄡ4
11
Try these two.
16
2=ᄡ
7 15
10 16ᄡ
Try these two.
• Divide the 10 and 15 by 5
• Make the 6 a fraction.
• Divide the 2 and 6 by 2.
16
2=ᄡ
7 15
10 16ᄡ
1 6
2 1=ᄡ
3
2
21
32=
3
1
3
2=
Make a mixed number.
2 31
-2
1
112
=
Work on Worksheet F4