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

You are not logged in.

- Topics: Active | Unanswered

**mandy jane****Member**- Registered: 2010-09-23
- Posts: 886

Is it 3 am I right

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 535

No. The denominators of the question are 3 and 4. What we need to do is convert those fractions so that the denominator is

the same. If we make the second one 3 then it will be difficult to work out (1/4) in thirds.

The best thing to do is get them into a form where they are (something / 12)

I got that number from 3 x 4 = 12

To get (2/3) in the form (something / 12) multiply top and bottom by 4.

To get (1/4) in the form (something / 12) multiply top and bottom by 3.

*Last edited by SteveB (2013-04-22 01:24:18)*

Offline

**mandy jane****Member**- Registered: 2010-09-23
- Posts: 886

Hi so is it 3/12 & then. 6/4 am I right?

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 535

That is not quite right, but you are getting there. (3/12) is one of the fractions, but the other is wrong. Try again ?

Hint: (1/4) = (3/12)

(2/3) = ????

*Last edited by SteveB (2013-04-22 01:28:32)*

Offline

**mandy jane****Member**- Registered: 2010-09-23
- Posts: 886

Is it 6/8 am I right?

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 535

No that is not correct. Try again ?

Offline

**mandy jane****Member**- Registered: 2010-09-23
- Posts: 886

Is it 8/6 am I right?

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 535

No the correct answer was that (2/3) = (8/12)

Remember that the other fraction was (3/12). So what is the answer to the original question ?

Offline

**mandy jane****Member**- Registered: 2010-09-23
- Posts: 886

I am finding this hard to do?

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 535

(2/3) + (1/4) = (8/12) + (3/12) = ????

The denominators are now equal. The numerators can now just be added.

Do not add the denominators though.

*Last edited by SteveB (2013-04-22 01:40:23)*

Offline

**mandy jane****Member**- Registered: 2010-09-23
- Posts: 886

Is it 11/12 am I right?

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 535

Yes that is correct. Now let us go back to Q2.

This was (1/5) + (1/3)

What would be a good denominator to use ?

Offline

**mandy jane****Member**- Registered: 2010-09-23
- Posts: 886

Is the denominator 5 & 3 am I right?

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 535

We need to get the denominators to be same. How could we do that ?

Offline

**mandy jane****Member**- Registered: 2010-09-23
- Posts: 886

Is it 3x5 =15

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 535

Yes correct.

So what is (1/5) in fifteenths ?

What is (1/3) in fifteenths ?

Offline

**mandy jane****Member**- Registered: 2010-09-23
- Posts: 886

Not sure what to do?

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 535

(1 / 5 ) = (3 / 15)

The reason for that is that I have multiplied top and bottom by the same number.

In general it is possible to multiply the numerator and denominator by the same number and the fraction is still the same.

You could try drawing a diagram to show this. Let us say you had a square. You divide it into 5 bits which are equal in size.

That represents (1/5) now try dividing the square so that each of the five equal bits are divided into 3 bits.

You can use this to prove that (1/5) = (3/15)

What is (1/3) equal to ?

*Last edited by SteveB (2013-04-22 02:01:25)*

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 535

I could make up an image file to illustrate the division into 3 and 5 and 15, but it will take about 10 minutes to set up.

Do you want to just take my word for it or would you like an illustration ?

Offline

**mandy jane****Member**- Registered: 2010-09-23
- Posts: 886

Could you do an illustration for me please

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 535

Right hopefully the image will display alright.

I have drawn a rectangle. Imagine that the whole of the big rectangle represents the number 1

Now imagine that we have divided this big rectangle into 5 equal bits. Each of these is (1/5).

Now imagine that we have divided this big rectangle into 3 equal bits. Each of these is (1/3).

The very small bits made by dividing the big rectangle into 15 bits are each (1/15)

The fraction (1/5) is really 3 of the very small bits so (3/15)

The fraction (1/3) is really 5 of the very small bits so (5/15)

Offline

**mandy jane****Member**- Registered: 2010-09-23
- Posts: 886

So is the answer 3/15 + 5/15 = 8/15 am I right?

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 535

Yes correct.

Do you want to have a go at Q3 ?

It was (1/3) + (5/6)

The answer is greater than one here, but the principle is the same.

Offline

**mandy jane****Member**- Registered: 2010-09-23
- Posts: 886

I have /18 am I right?

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 535

Yes you need to work out how many eighteenths each of the fractions is.

So (1/3) = ( something / 18 )

and (5/6) = ( something else / 18 )

Offline