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maths whizzes is this wrong?

(20 Posts)
CapricaSix Sat 30-Aug-08 22:49:53

Am redoing the Are you ready for Level 1 Science? test on the OU website. Here's the question:

A runway has length 1.5 km and width 60 m. What is its area? Your answer should include appropriate units

So my answer was 90 km2.

Here's their answer:

Your answer is still incorrect.
1 km = 1000 m,
so 1.5 km = 1.5 × 1000 m = 1500 m.
Then area = length × width
= 1500 m × 60 m
= 90000 m2
This could also be given as 0.090 km2.

Am I just totally confused or is 0.090 km2 just WRONG??? Surely if 1 km = 1000 m, 90,000 m IS 90 km?

differentID Sat 30-Aug-08 22:52:29

it looks like their answer is wrong.

Bowddee Sat 30-Aug-08 22:54:06

Either they're wrong or I'm missing something here.

CapricaSix Sat 30-Aug-08 22:55:35

angry, also <<smug>> grin

Threadwworm Sat 30-Aug-08 22:58:44

1km2 = 1000m x 1000m

So 90 000m2 = 0.09km2

KatyMac Sat 30-Aug-08 23:00:04

I'm confused

TotalChaos Sat 30-Aug-08 23:00:25

they are right - as it's 1.5 km x 0.06 km, not 1.5 km x 60 km.

ihearthuckabees Sat 30-Aug-08 23:00:31

Mmm, not sure about this, but if you do it the other way around i.e. using km, then it's:

1.5km x 0.06km

which would equal 0.09km2.

So it must be something to do with the fact the answer is squared. Yes, 9000m=90km, but 9000m2 is not 90km2, IYSWIM.

WilfSell Sat 30-Aug-08 23:01:56

90 km squared is wrong...

Think about it, would imply 90 squares, each a kilometre square in itself... Far too huge...

A plane would have to drive for miles and miles to the end of the runway...

KatyMac Sat 30-Aug-08 23:02:02

It would be 90km2 if it was 6okm wide

Because a sqkm is 1,000,000 m2?

I thought?

WilfSell Sat 30-Aug-08 23:04:02

Yes, but it is 6 m wide not 6 km...

Threadwworm Sat 30-Aug-08 23:04:06

Exactly. OU website is right

thumbwitch Sat 30-Aug-08 23:04:18

ah yes, threadworm has it. This is the age old confusion of squaring decimal places and not believing the result could possibly be what it is because it is counter-intuitive.

If you do it the other way,

60m = 0.06km.

0.06 x 1.5 = 0.090sqkm.

6 x 15 = 90 as you have worked out, but then you have to take into account that there are 3 figures to the right of the decimal point in the equation, so there also have to be 3 figures to the right of the decimal point in the answer.

WilfSell Sat 30-Aug-08 23:04:27

sorry - 60, not 6 m...

WedgiesMum Sat 30-Aug-08 23:04:29

You are right to say that 90,000m is 90 km BUT when you sqaure something you have to think about all the squares that make up the inside of that square. So 1km2 has 1000x1000 square metres in it which is in fact 1million m2 and their answer is correct - did I explain ok or did I confuse it further??

thumbwitch Sat 30-Aug-08 23:04:53

x-posted - took too long to type!

CapricaSix Sat 30-Aug-08 23:26:49

Yes. I see. Bollocks.
So I'm not ready for Level 1 Science then! grin

KatyMac Sun 31-Aug-08 09:46:46

You don't have tp get all of them right do you?

CapricaSix Sun 31-Aug-08 09:50:56

no it's fine, a couple of months ago when i did the test I was like oh shit cos i didn't even know what half of them were talking about (though there were vague memories from GCSE)! But since revising some of the maths (in the sciences good study guide) it's all coming together! I was redoing it to see if i felt any better about it, and I do!

KatyMac Sun 31-Aug-08 18:54:35

You had me worried

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