How to work out percentages. still stuck lol

jmoore · 2008-01-23 00:35:25

hey all,

I was wondering how do i work out percentages from money for example as shown below.

What percentage of £60 is £9?

In a police HQ car park there are 140 vehicles. 20% of these are police vehicles. How many are non-police vehicles?

also....

How many 7 x 7cm tiles are needed to cover an area that measures 84 x 84cm?

is the right answer this 7*12 = 84, then 7*12 = 84 then 12*12 = 144 so i should need 144 tiles

Last edited by jmoore (2008-01-23 00:45:25)

Jai Ganesh · 2008-01-23 01:55:21

Answer to first question:-

The answer is 15%.

For the second question, the answer is 80% of 140.
This is because 100% - 20% = 80%.
80/100 x 140 = 112.

The third question has been attempted correctly by you, the answer is 144 tiles.

NullRoot · 2008-01-23 02:02:24

When you're asking yourself, "What percentage of number1 is number2?" then what you want to do is work out this:
number2 ÷ number1

In your example you want to know "What percentage of 60 is 9?", so you need to work out what 9 ÷ 60 is. Can you see how I used the rule above to get that?

Normally your answers will be a decimal. Working out "What percentage of 100 is 10?", for instance, is:
10 ÷ 100 = 0.1

Let's call this type of percentage the "Useful Percentage" because it's very useful (as you'll see below).

Normally you'll see percentages written like 10% or 20%, and so on. Let's call that type of a percentage the "Pretty Percentage" because it looks pretty and it's the style most people like to see.
This is the first use of our Useful Percentage. To obtain the Pretty Percentage, multiply the Useful Percentage by 100.
So... What percentage of 100 is 10? First, we obtain the Useful Percentage:
10 ÷ 100 = 0.1

Next we turn it into a pretty percentage: 0.1 × 100 = 10%
Now try it with your question "What percentage of 60 is 9?". First get your Useful Percentage and then find the Pretty Percentage.

NullRoot · 2008-01-23 02:13:59

The other use for a Useful Percentage is to find out the answer to questions like "What is 30% of 150?"

To obtain the Useful Percentage from the Pretty Percentage you must divide the Pretty Percentage by 100.
So 30% is our Pretty Percentage. To make it useful we divide by 100 like this:
30 ÷ 100 = 0.3

Now here's how we use it. We want to know what 30% of 150 is. To get the answer you multiply the number (150) by the Useful Percentage.
150 × 0.3 = 45

So 30% of 150 is 45.

Taking your example, you know that 20% of the cars belong to the police. What is 20% of 140?
First, obtain the Useful Percentage: 20 ÷ 100 = 0.2
Second, multiply it to your other number: 140 × 0.2 = 28

That means 28 of the cars belong to the police. That means the rest must belong to other people.
140 cars - 28 belonging to police = 112 cars belonging to other people

John E. Franklin · 2008-01-24 15:40:18

Your answer is right on the 84 by 84 area with 7 by 7 tiles. 12 x 12 = 12 * 12 = 144 Good Job!!

jmoore · 2008-01-26 05:04:23

sorry for taking long to reply back thanks for you help i can do most maths questions but when percentages and decimals etc.. are involved then that when i get stuck

John E. Franklin · 2008-01-26 05:14:34

Here's some info to show how easy decimals are.
See how they are the same with the decimal moved out to the right so it dissapears into whole numbers.
8 x 7 = 56
.8 x .7 = .56

4 x 3 = 12
.4 x 3 = 1.2

2 x 7 = 14
.02 x 70 = 1.4

A line about the number TEN.
Also, 10 = 10. = 10.0 = 10.00 = 1d.0 where d is a digit equal to 0 or close enough we call it zero.

jmoore · 2008-01-27 04:52:11

i seem to be having trouble dividing 60 by 9 in my head as that is what i need to be able to do i can get 6.666.... but not 0.15

mathsyperson · 2008-01-27 05:28:46

60 divided by 9 is 6.666...
What you need to do though, is 9 divided by 60.

jmoore · 2008-01-27 06:36:43

how would i go about doing that with long division? 9/60 all i know is it goes in 1 with 3 left over

mathsyperson · 2008-01-27 07:02:29

If you find it easier, you could alternatively do 0.9/6.

jason890 · 2009-01-04 03:21:26

what is percentage is 80 of 2000000

Daniel123 · 2009-01-04 03:33:50

(80/2000000 x 100)%

Jai Ganesh · 2009-01-04 03:35:41

The question is NOT clear.

Is it, what is 80 percentage of 2000000?

or

what percentage of 80 is 2000000?

random_fruit · 2009-01-04 04:58:22

One of my children (all now grown into sensible adults, but that's another story) finally understood percentages when I talked with her about it in terms of money.

First, one percent of one pound is one penny. (This is £ sterling in UK, but applies just as well to Euros and cents, Dollars and cents, etc).

Second, a one percent increase applies to every pound of wages earned in a week. So, for examples:
£1/week + 1% gives £1.01/week
£2/week + 1% gives £2.02/week
£1/week + 2% gives £1.02/week
£2/week + 2% gives £2.02/week
We discussed what percentage her pocket-money should go up next birthday in similar fashion. She soon got the idea from the pattern above.

Finally we discussed reductions by a percentage. At a sale in a shoe shop, some shoes were advertised as 25% off. I said, it probably meant that those shoes now cost 75p for each £1 they used to cost before the sale. We did some examples:
£1 gone down to 75p
£2 gone down to £1.50
£3 gone down to £2.25
£10 gone down to £7.50
£40 gone down to £30.
On the last she said "Huh, I can tell how often you buy womens' shoes" but I protested "But Dads don't buy womens' shoes."

A few days later she followed up with: Why did you say "it probably means"? I joked that some shop-keepers with a particularly keen desire to emphasise the value-for-money of their goods, could compute the percent reduction another way. I said, if a pair of shoes now cost £50 and used to cost £100, could that be computed as 100%? She said "no" but I reminded here that the reduction (£100-£50) was £50 which was clearly reduction-in-price/original-price = £50/£50 and therefore 100%. She said "that's cheating" and I said it was not beyond the guile of some. I'd like to think that UK trading standards departments have an opinion about this, but I have no experience.

Finally, whenever I hear a percentage being mentioned on the news: "house prices in the UK have fallen 12% over the last year, says" I have three questions: (a) show me the input data (b) how do you justify the computations and (c) who wishes to prove what with it.

In my opinion, percentages are often poorly understood by many people and this results in a mis-use of them as heresay and opinion, and not useful arithmetic. I think it would be a good idea if only interest rates on loans and savings, and rates of tax, were expressed in percentages.

Hey, that's my education bit (and rant) over, hope some of you enjoyed it.

careless25 · 2009-01-04 05:13:42

£2/week + 2% gives £2.02/week

That sounds wrong to me....
£2 * 2% = 0.04
£2/week + 2% gives £2.04/week

JaneFairfax · 2009-01-04 07:26:21

ganesh wrote:

The question is NOT clear.
Is it, what is 80 percentage of 2000000?
or
what percentage of 80 is 2000000?

Thats the problem with people like jason890. If they dont even learn to state their question properly, they wont understand the question itself; in that case, how on earth are they going to understand the explanations we give them? Such students are simply wasting our time I have no patience with any of them!

darkest_salem · 2009-01-06 12:44:23

Maybe for example: 3/34 = x/100

mdshuiew · 2009-02-10 07:23:18

jmoore wrote:

hey all,
I was wondering how do i work out percentages from money for example as shown below.
What percentage of £60 is £9?

In a police HQ car park there are 140 vehicles. 20% of these are police vehicles. How many are non-police vehicles?

also....
How many 7 x 7cm tiles are needed to cover an area that measures 84 x 84cm?
is the right answer this 7*12 = 84, then 7*12 = 84 then 12*12 = 144 so i should need 144 tiles

i am also stuck on it

mathsmypassion · 2009-02-10 11:04:17

Understanding percentage is a bit of a challenge. Once you get them you will never forget.

For the first problem:
The initial amount is $60.
10% of this amount is ... $6. Clear enough?
So $9 = $6 + $3 in fact 10% + 5% (1/2 of 10%) = 15%
The answer: 15% of $60 is $9
This is the best way to start to understand percentages, by thinking.

Last edited by mathsmypassion (2009-02-10 11:04:52)

Math Is Fun Forum

#1 2008-01-23 00:35:25

How to work out percentages. still stuck lol

#2 2008-01-23 01:55:21

Re: How to work out percentages. still stuck lol

#3 2008-01-23 02:02:24

Re: How to work out percentages. still stuck lol

#4 2008-01-23 02:13:59

Re: How to work out percentages. still stuck lol

#5 2008-01-24 15:40:18

Re: How to work out percentages. still stuck lol

#6 2008-01-26 05:04:23

Re: How to work out percentages. still stuck lol

#7 2008-01-26 05:14:34

Re: How to work out percentages. still stuck lol

#8 2008-01-27 04:52:11

Re: How to work out percentages. still stuck lol

#9 2008-01-27 05:28:46

Re: How to work out percentages. still stuck lol

#10 2008-01-27 06:36:43

Re: How to work out percentages. still stuck lol

#11 2008-01-27 07:02:29

Re: How to work out percentages. still stuck lol

#12 2009-01-04 03:21:26

Re: How to work out percentages. still stuck lol

#13 2009-01-04 03:33:50

Re: How to work out percentages. still stuck lol

#14 2009-01-04 03:35:41

Re: How to work out percentages. still stuck lol

#15 2009-01-04 04:58:22

Re: How to work out percentages. still stuck lol

#16 2009-01-04 05:13:42

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#17 2009-01-04 07:26:21

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#18 2009-01-06 12:44:23

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#19 2009-02-10 07:23:18

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#20 2009-02-10 11:04:17

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