Math Is Fun Forum

All ten of those are correct. Well done.

Looks like it's back to ratios then.

Okay. Here is a question to do with ratio in a different context:

Let us suppose that there is a sum of money £120.00  (120 pounds) and it has to be shared in a 1:2 ratio
For every 1 pound that Edward gets Sarah is given 2 pounds. So the ratio amount given to Edward: amount given to Sarah is 1:2
Calculate how much money in pounds Edward and Sarah should be given to make this happen.

Yes that is correct. Good.

Let's go back to division: 3.9 divided by 100 ?

Yes that is correct. However it is more usual to write 0.47 rather than 00.47

Right how about:  34 x 100 ?

Correct.

Now how about this:  47 divided by 100 ?

I think I will ask you another one now:

5.6 divided by 10 ?

You have divided by 10 rather than multiplied by 10.

Same again here....

and here

Here you have divided by 10, but you were supposed to times by 100.

Here you have divided by 100.

Here you have simply added point zero on the end. Doing this does not actually change the value of the number, but is sometimes
useful to help with a calculation. In other words 65 = 65.0

I think the problem here is understanding the question. Do you want to have another attempt at those?

SECOND EDIT:
I have sent 2 emails to you (Mandy) about this and I hope they have been of some help. Just in case they have not got
through here are a few notes on multiplication by 10 and 100, and division by 10 and 100.

Let us consider a number like 27.34

It can be thought of as 2 tens, 7 units, 3 tenths and 4 hundredths as shown below:

    tens    units   tenths    hundredths
      2         7   .    3               4

To divide by ten the numbers go this way one space ------->
<--------- To multiply by ten the numbers go this way one space.
When we divide by 10: tens become units, units become tenths, tenths become hundredths, hundredths become thousanths ......(etc)
When we multiply by 10: hundredths become tenths, tenths become units, units become tens, tens become hundreds ........(etc)

So if we successively divide by 10:
27.34 becomes 2.734 then 0.2734 then 0.02734 then .....(etc)

If we successively multiply by 10:
27.34 becomes 273.4 then 2734 then 27340 then 273400 .....(etc)

Do not spend too long on these questions. If they are taking more than about 20 seconds each to do then something is wrong.

Can you give me an idea of how many questions to set?

Right the original ratio was 3 parts yellow to 7 parts blue. Or 3 : 7

So yellow first:  3 x 7 = 21
Now blue: 7 x 7 = 49

Quick check:  21 + 49 = 70

There are two things here that you need to revise possibly:
(1) Times tables
(2) Division by 10 (and for that matter multiplying by 10)

70 divided by 10 is 7 

Each time you have a multiplication in the form: a x b = c
This means that  c / a = b
and also c / b = a
(We do need to take care to avoid divisions by zero here, but that is another story)

So here  7 x 10 = 70       70 / 10 = 7       70 / 7 = 10

No that is not correct. I think this is a times tables problem. 5 x 10 = 50 and 10 x 10 = 100 somewhere inbetween these two
guesses lies the answer. I don't want to simply tell you the answer because this is good practice for you.
Do you want to try again?

Right. The thing that I am calling an old total is the same (3 + 7 = 10). However I have given you a different number for the
new total. The new total is 70. What is the scaling factor in this case ?