Maths question that is troubling me help please!

PikKOn · 11 Dec 2009 at 13:50

Hi all, I am having some trouble with a fairly simply maths question that maybe I am working out wrong. Heres the question:

Total number of drug offences this represented a 15% increase on last year's figures. How many drug offences were commited last year?

Drug offences for men 20%
Total offences for men 379,000(100%)

Drug offences for women 10%
Total offences for men 88,000(100%)

Possible answers: 72,245 or 73,585 or 74,415 or 76,085 or 78,905

-----------------------
I did 379,000 + 88,000 = 467,000
20 + 10 = 30%

0.30 * 467,000 = 140,100 (this gives me the current value)

How do I work out the value before it rose 15%? I imagined this could be done by simply working out 15% of 140,100 and then minus that value from 140,100?

Hoping theres a math guru here on the forums

Dist · 11 Dec 2009 at 13:54

75800 drug offences men
8800 drug offences women
84600 total

84600 / 1.15 = 73565 last years total

Wicksta · 11 Dec 2009 at 13:55

Wait around, I'm sure mattheman will be about to give you a hand shortly.

Greebo · 11 Dec 2009 at 14:00

Dist said:
75800 drug offences men
8800 drug offences women
84600 total

84600 / 1.15 = 73565 last years total

You're 100% right......just a shame it's not one of the answers :confused:

marc_howarth · 11 Dec 2009 at 14:09

PikKOn said:
I did 379,000 + 88,000 = 467,000
20 + 10 = 30%

0.30 * 467,000 = 140,100

Here's a mistake,
20% of 379000 = 75800
10% of 88000 = 8800
add them together to get 84600

you can't just add the totals and the percentages together, you have to work them out seperately

Vixen · 11 Dec 2009 at 14:14

PikKOn said:
How do I work out the value before it rose 15%?

The previous figure was 85% of the current one, so multiply by 0.85.

WillyNelson · 11 Dec 2009 at 14:28

(379,000*.2)+(88,000*.1) to give you the total numbe of drug offences this year = 84,600/1.15 = 73,565

The possible answers are wrong.

WillyNelson · 11 Dec 2009 at 14:30

Vixen said:
The previous figure was 85% of the current one, so multiply by 0.85.

No, it was 87% of the current one

current = previous*1.15
current/1.15 = previous
1/1.15=0.87

sammo62 · 11 Dec 2009 at 14:31

Are you doing Civil Service application tests? very much looks like it.

WillyNelson · 11 Dec 2009 at 14:33

ignore

hood1971 · 11 Dec 2009 at 14:34

This year drug for men = 379000* 20% = 75800

This year drug for women = 88000 * 10% = 8800

Total = 84600

Last years figures = a
a + a(15/100) = 84600
100a + 15a = 8460000
a = 73565

Which isn't one of your answers so not helpful unless you coped the 73585 wrongly

craptakular · 11 Dec 2009 at 14:36

I don't wish to be offensive, as that isn't my intention but I found the Keystage 2, keystage 3 and keystage 4 purple revision books really useful for brushing up on maths.

I'm 26 now and those keystage revision books were exactly what I needed.

daniel_owen_uk · 11 Dec 2009 at 14:38

100% correct willy

You can't add the total and then multiply by sum of percentages as they are percentages of different values.

You can't multiply by .85 to get 15 less (ie find 15%) as you are not trying to get 15% less, you are trying to get the value before 15% was added.

If you have £100 and add 15% you get £115

If you then get 85% of 115 you would be left with £97.75 not £100

Had this with some VAT issues at work recently.

PikKOn · 11 Dec 2009 at 15:10

Sorry it was 73565 as a possible answer. It is a civil servant test

PikKOn · 11 Dec 2009 at 15:30

Thank you everyone, I know where to post my math queries now

Again thank you all for your posts I really appreciate your guidance and help.

WillyNelson I believe got the correct answer and looking at it, it was pretty simple but I thought I had to multiple by 1.15 as opposed to dividing by it :\

Mr.E. · 11 Dec 2009 at 15:40

Probalably a bit late. I'm useless at maths but as the current VAT rate is 15% I know how that works out.

To work out the vat on a total figure you x3 then /23

So my answer is 73566 total !

PikKOn · 11 Dec 2009 at 16:07

Oxy said:
I don't wish to be offensive, as that isn't my intention but I found the Keystage 2, keystage 3 and keystage 4 purple revision books really useful for brushing up on maths.

I'm 26 now and those keystage revision books were exactly what I needed.

Hi Oxy I will be giving that a go then mate, I need some brushing up

Destination · 11 Dec 2009 at 16:36

PikKOn said:
Sorry it was 73565 as a possible answer. It is a civil servant test

Ok, a civil service test?
Your entire methodology is fundamentally flawed.
At its most basic level its completely wrong.
I think starting with the keystage 2, 3 and 4 maths books would be the best way to begin.

I actually find this quite concerning.