7 shortcuts for solving fractions in record time
Welcome to MooMooMath Today we are going to
learn tricks with fractions. This video covers all 7
Trick number one,the criss cross method. This is an easy way to add two fractions without
working to hard to find a common denominator The first step is to multiply the denominators
together. 4×6=24 Now you will use what we call the “Criss-Cross Method” 6×3=18 and
4 x 1=4 . Add these together to get the numerator which equals 18+4=22 for the numerator.
Bring the 24 over and then you just reduces to 11/12 and that is our final answer. So
that is the criss- cross method for adding fractions. A con of this method is that it
is a shortcut and you are not learning the actual reasons for everything.
Let’s do a more traditional method of adding fractions. We will just multiply the denominator
which is 4×5=20 Now we will figure out our multiplies. I take 20 which is my new denominator
and divide it by the original denominator4 So 20 divided by 4=5 So the first fraction
I will multiply by 5 and the second fraction I will multiply by multiplier of 4.Once I
multiply by those my numbers my denominator becomes a 20,but my numerator becomes a 10
+ 12 and that becomes 22/20,which reduces to 11/10 or you can change this fraction to
a mixed number by dividing by 10 which equals 1 1/10. and this is my final answer as a mixed
number. Fraction trick number 3 KCF which is the Keep
it,Change it Flip it method. and you use this to divide fractions. Lets look at the two
fractions a/b divided by c/d You will now use Keep Change Flip to divide this fraction.
You will take the first fraction and keep it. That is what the K stands for. The C stands
for change and you will change from division to multiplication. The F stands for flip it,and
you take the reciprocal of the last fraction.and it becomes d/c. Now from here you just multiple
the fractions straight across and end up with ad/bc. Here is a quick example with numbers.
Take 1/2 divided by 3/4 I keep the 1/2.I change the division to multiplication,and I flip
the 3/4 to 4/3 I then multiply straight across and end up with 4/6 and reduce the answer
and end up with 2/3 To reduce the fraction I’m just dividing by a common factor 2. That
is how I use trick 3 Keep it Change it Flip it Rule.
Trick # 4 Knowing the lingo. We are going to learn some terms in fractions. What is
a vinculum? It
is the line between the numerator and your denominator. The top of the fraction is the
numerator and the bottom is the denominator,and the bar in the middle is a vinculum.Now you
know the word for that bar between the 2 numbers when you divide.
Trick 3 5 The Ladder Method This is very useful when you are given two
numbers and you are trying to find the greatest common factor (GCF) or the least common multiple
(LCM) Some people call this the cake method.Let’s take 16 and 24. I will draw a bar underneath.
A sideways L Next I will look for a prime factor that will divide evenly into both numbers.
2 will divide into both numbers and I get 8 and 12. Then draw a new line,and find a
prime factor that will divide into these two numbers. 2 goes again 2 goes into 8 4 times,and
goes into 12 6 times. Draw a new bar and find a new prime factor. 2 goes a third time 4
divided by 2 is 2 and goes into 6 3 times. I now do not have another prime factor. so
I put a 1. So what do I have left. On the left side I have multiple these prime numbers
together 2x2x2x1=8 and this is my greatest common factor. that divides both into 16 and
24. Now to find my LCM I will take the first list of prime numbers plus my remainder and
multiply all those numbers. 2x2x2x1x2x3=2×2=4 4×2=8 8×2=16 16×3=48 and that is my least common multiple (LCM)
Trick #6 This is called the circle method. It is used to turn a mixed number into an
improper fraction. We will start at the denominator and multiple in a circular direction. So I
will take 2×3 and multiply this first. I then will take this result and add the numerator.So
this will be 2×3=6 plus 1 is 7,which becomes my new numerator and I keep my denominator
a 2. The 31/2 becomes 7/2 42/3 3×4=12 and then add 2 which becomes
14/3 That is my circle trick to convert.
Trick # 7 Is just
to memorize. Try to be familiar with these 12 fractions and their decimal equivalents
you will have a good number sense of where numbers should fall between the value of 0
and and 1. So the best thing I can tell you is to get some flashcards,go on quizlet and
they may be on quizlet and become familiar with these fractions. 1/4=.25 The way I remember
the ones with a denominator of 4 is think of quarters If I 1 quarter I have 25 cents.
If I have 3 quarters I have 75 cents. A 1/2 is .50 or half a dollar. 1/5 is .20 because
it takes 5 twenty’s to make whole. Now the thirds fall in another family. 1/3=.333
repeating.but 2/3=,333 doubles which is .666 repeating. 3/5 is just adding .20 to
2/5 and add .20 to 3/5 and get .80 . We are adding .20 each time. The 8ths are a little
tricky to remember. 1/8 is .125 and 3/8=.375 5/8=.625 and 7/8=.875 These are the trickiest
to remember. Get comfortable with these. Try to write the patterns and write these fractions
down and improve your number sense. This helps and when you see a whole number like 5.375
you know that is really 5 3/8 Those are your 7 fraction tricks to remember.
Hope this video helped.