Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

You are not logged in.

- Topics: Active | Unanswered

**SteveB****Member**- Registered: 2013-03-07
- Posts: 574

Right OK. Percentages.

Now, if I have a number like say 50 and you had to add 10% would you know how to do that ?

(I am trying to get an idea of how much you know already)

Offline

**mandy jane****Member**- Registered: 2010-09-23
- Posts: 1,126

no i do not know how to do that ok? so now want?

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 574

Right. OK. Now I will give you a worked example for that. Some people reading this would know at once the answer, but

I will explain how I would think about this question (in a way that works when the numbers are not quite so nice).

The percentage 10 % can be thought of as being like the decimal 0.1

If you say "calculate 10 percent of" something then you mean calculate 0.1 times something.

In other words we are trying to work out 50 x 0.1 and then adding that to 50.

So I happen to know that 50 x 0.1 = 5

So that means that 10% of 50 is in fact 5

Then when you add that on to the number 50 you get 55

So in answer to my original question the answer is 55.

Now are you happy with the concept of multiplying by a decimal like 0.1 ?

Can you see that if you multiply by 0.1 you are dividing the number by 10 ?

EDIT:

*Last edited by SteveB (2013-05-09 07:15:53)*

Offline

**mandy jane****Member**- Registered: 2010-09-23
- Posts: 1,126

yes i think i understand? can you make sure please?

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 574

Right here is a related question to test you on multiplying by a decimal:

What is 20 x 0.2 ?

Offline

**mandy jane****Member**- Registered: 2010-09-23
- Posts: 1,126

no i looked at it again and no i don't understand it at all ok?

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 574

When I look at the number 0.2 I would automatically know that it is one fifth, but that is not necessarily obvious.

You can re-write 0.2 as a fraction by the fact that it is the same as 2 tenths.

So using some Latex:

*Last edited by SteveB (2013-03-20 05:30:08)*

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 574

I will have to try to get better at using Latex. I am struggling with using it to write fractions.

Right now: Here is another question ..... What is one fifth of 20 ?

So what is 0.2 x 20 ?

What is 20 % of 20 ?

Offline

**mandy jane****Member**- Registered: 2010-09-23
- Posts: 1,126

is it 22then?

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 574

Okay here are a few notes on that:

one fifth of 20 is:

*Last edited by SteveB (2013-03-20 05:31:52)*

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 574

Have you been taught about multiplying fractions ?

*Last edited by SteveB (2013-03-20 07:41:48)*

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 574

What whole number is the fraction ....

equal to.

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 574

Okay the answer is that 20 should be divided by 5. The answer is four.

That is to say:

Any number divided by 1 is itself.

Therefore:

*Last edited by SteveB (2013-03-20 05:35:09)*

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 574

20 % can be thought of as the same as the following fraction:

Try cancelling or simplifying this fraction as far as you can go. What do you get ?

Offline

**mandy jane****Member**- Registered: 2010-09-23
- Posts: 1,126

to answe 686 no i have not been taough multiply fraction i don't think?

Offline

**mandy jane****Member**- Registered: 2010-09-23
- Posts: 1,126

20

---

100

2

---

10

1

---

5

am i right?

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 574

Sorry about that my computer crashed so it then wasted several minutes rebooting.

I think we had better discuss multiplication of fractions. This is relevant to percentages to a certain extent.

Right let us take an example:

The answer is to multiply top and bottom numbers together....

So the numerators (top) are 2 x 1 = 2

The denominators (bottom) are 3 x 2 = 6

So the result is:

This simplifies to:

*Last edited by SteveB (2013-03-20 05:37:32)*

Offline

**mandy jane****Member**- Registered: 2010-09-23
- Posts: 1,126

ok could i have som fraction for me to do befor tomorrow ok?

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 574

Your post # 691 is correct. Good. Well done. I will give you a chance to read the next post.

*Last edited by SteveB (2013-03-20 05:38:12)*

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 574

Right I will give you a few fraction multiplication problems. Remember not to confuse adding and multiplying fractions.

Cancel or simplify as far as possible.

(At the time of posting I was unable to use Latex to display things like this in a good readable fashion

I have now been taught by Bob to do this properly. If you look further back, Mandy, you will find that

I have gone through it and tidied up the earlier fractions. They will hopefully be easier to read.)

*Last edited by SteveB (2013-03-20 05:46:44)*

Offline

**mandy jane****Member**- Registered: 2010-09-23
- Posts: 1,126

did you read post 693 if so do you have an answer for me?

Offline

**mandy jane****Member**- Registered: 2010-09-23
- Posts: 1,126

see you at 2.00pm on here tomorrow by

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 574

Another quick question for you to answer:

*Last edited by SteveB (2013-05-09 07:21:35)*

Offline

**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,789

hi SteveB and Mandy

Here is a way to improve your Latex.

http://latex.codecogs.com/editor.php

Bob

*Last edited by bob bundy (2013-03-20 05:22:19)*

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 574

Mandy I recommend that you look through this entire page again I have updated some of my posts to improve readability.

Offline