Just one sec...
Hey! Sign in to get help with your study questionsNew here? Join for free to post

Reverse Percentages

Announcements Posted on
    • Thread Starter
    Offline

    ReputationRep:
    The question is:
    In a class there are 9 people absent. This is 20% of the class
    How many are there in the class when no-one is off ill?

    so to work out i did: 1.8*9=16.2

    but 10% of the question is 4.5 and 4.5*10= 45 (Half of 20 is 10 and half of 9 is 4.5)

    so i recon 45 is the answer but how do I work it out the first way?
    Offline

    ReputationRep:
    (Original post by S_Kid)
    The question is:
    In a class there are 9 people absent. This is 20% of the class
    How many are there in the class when no-one is off ill?

    so to work out i did: 1.8*9=16.2

    but 10% of the question is 4.5 and 4.5*10= 45 (Half of 20 is 10 and half of 9 is 4.5)

    so i recon 45 is the answer but how do I work it out the first way?
    Yes, 45, is the correct answer.

    Lets say that the total number of students in the class are  \displaystyle x

    So we can form the equation as below,
     \displaystyle \frac{20}{100} \times x = 9
    Offline

    ReputationRep:
    (Original post by S_Kid)

    so i recon 45 is the answer but how do I work it out the first way?
    What do you mean "the first way"

    Where did 1.8 come from

    9/0.2 = 45
    Offline

    ReputationRep:
    (Original post by TenOfThem)
    What do you mean "the first way"

    Where did 1.8 come from

    9/0.2 = 45
     0.2 \times 9 = 1.8
    Offline

    ReputationRep:
    9 = 20%
    45 = 100%
    Offline

    ReputationRep:
    (Original post by raheem94)
     0.2 \times 9 = 1.8
    Maybe but ... why would they then do 1.8x9?
    Offline

    ReputationRep:
    If 9 equals 20% then 100% will equal 9 multiplied by five. This is 45. The reason why you multiply by 5 is because you want to get from 20% to 100% (the full amount).
    Offline

    ReputationRep:
    (Original post by TenOfThem)
    Maybe but ... why would they then do 1.8x9?
    There is no reason to do this. I was just telling you that this was probably the way in which the OP worked out 1.8, however, it looks wrong to do this.
    Offline

    ReputationRep:
    (Original post by raheem94)
    There is no reason to do this. I was just telling you that this was probably the way in which the OP worked out 1.8, however, it looks wrong to do this.
    Yeah .. the method was clearly wrong I was just trying to figure out what their thinking was
    Offline

    ReputationRep:
    Seriously, if you can't do this, go to primary school.
    Offline

    ReputationRep:
    (Original post by AGrumpyMole)
    Seriously, if you can't do this, go to primary school.
    The OP is asking for help, and you aren't being of any help by giving such harsh opinions.

    There is no shame on asking a simple question, he is at least trying to learn it.
    Offline

    ReputationRep:
    (Original post by AGrumpyMole)
    Seriously, if you can't do this, go to primary school.
    It is only easy if you know the answer.

Reply

Submit reply

Register

Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  3. this can't be left blank

    6 characters or longer with both numbers and letters is safer

  4. this can't be left empty
    your full birthday is required
  1. Oops, you need to agree to our Ts&Cs to register
  2. Slide to join now Processing…

Updated: March 31, 2012
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

Poll
How do you sleep?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read here first

Equations

How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups
Study resources

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22

Registered Office: International House, Queens Road, Brighton, BN1 3XE

Quick reply
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.