are you quick?

[bartholomew]

hi!
I have the following problem. I need to pass an advanced numeracy test and I was wondering if there is any intelligent way of solving this problem. You have only 20 seconds, you cannot use a calculator or paper.

Out of 23,850 people in a cricket ground, 30% had bought tickets in advance. How many people paid to get in on the day.


Now, one way is to find out what is 10% then x3 and subtract this from 23850. however this method is too slow and it is too easy to make an error. Any other suggestions welcome.

Thanks

Bart

[osprey88]

find 10% and multiply by 7, wil give you the answer. still not easy, but i don't think there is an easy way.

[chazza]

Multiply by 0.7

[squarebear]

and you can multiply 23850 by 0.7 in your head in 20 seconds?!

[dundurn]

It's not a "simple" method but I can do it in my head - 23850 is almost 24000, 150 short. 7 x 150 is 1050 so whatever answer you get from calculating 70% of 24000 you're going to have to subtract 1050 from it. Forget the thousands until you need to use them. Multiply 24 by 7, gives 168 = 16800 less a 1000 = 15800 less 50 -15750. Makes sense to me, but may not work for you.

[nightmare]

Dundurn
you multiplied the 150 by seven instead of 0.7, so yopu need to subtract 105, giving the correct answer of 16695

[stewey]

Could it be a sort of trick question; "How many people paid to get in on that day?" Surely they all paid to get in on that day? The question was not "how many people paid on that day to get in?"

[naomi24]

Stewey, Bart asked are you quick? - and the answer is yes you are. :o)

[kempie]

Not quite stewey.

Your changing of "the" to "that" makes a subtle difference to the meaning of the original question "How many people paid to get in on the day?"

[kwicky]

(7 x 24 x 10^2) - (7 x 15) = 16695

[chazza]

Actually yes I can, just multiply it by 7 and move the decimal point!

[stewey]

You're right, kempie; I didn't realize that I had changed 'the' to 'that' when I wrote my response.

[dundurn]

nightmare - mea culpa - my first instinct was right - I'll stick to using spreadsheets!

[Oldboy913]

divide by 100
multiply by 7
10 seconds?

[studyone]

hi im only twelve and all you have to do it times it by 0.7 and it gives you 16695
now thats math !
and i didnt even have to use a calculator or paper

[kwicky]

He did say not to use a calculator or paper so if you can multiply such a large number in your head you must be brainier than gunga din. That is why the numbers should be broken down so mere mortals can handle it.