Monday 22nd March 2021
LC- Finding percentages.
Last week we looked at finding percentages when we compared the amount with a fraction out of 100. However, what would happen if the denominator was not 100?
Have a look at the following question and discuss it with the person next to you. What knowledge do we have that could help us?
Well done. The first one as a fraction would be 93 out of 300. We need the denominator to be 100 and not 300, so what would we have to do? That's right, we would divide by 3. Remember what we do to the bottom, we would do to the top.
What would we need to do for the other examples?
Can we find a number that would be easy to turn into 100? What if we know how many out of 50 pupils got an A? Can that help us? How can we work that out? What would that be as a fraction? How many groups of 50 are there in 250? How can we use this to find out how many got an A out of 50? What would 80 divided into 5 groups be? Would that be easy to convert into a percentage? What would you do?
So for this example, we needed to look at 250 and think of a factor that we could easily turn into 100.
50 fits in to 250 and can be easily turned into 100.
So 250 divided by 5 = 50 and then 80 divided by 5 = 16.
We now have a fraction of 16/50. We still can't find a percentage so what would we need to do next?
Multiply by 2 to get 32/100. Now we can do it.
What about the last example of 42/120?
Is there a number that is a factor of 120 that we could then turn into 100?
So 20 is a factor of 120 that could easily be turned onto 100. There are 6 20's in 120 so we also divide 42 by 6 and get 7.
We now have a fraction of 7/20. We then need to multiply by 5 to get a fraction out of 100.
Now we have done all this, can we answer the original question?
It does get easier the more we do it!
Let's work on the guided practice.