# Help Needed From You Mathematicians!

babybell 12:30 04 Jun 2009
Locked

I was scouting the BBC wesbite and decided to take the GCSE Maths quiz:

My issue is with question 6:

9.02 x 10-3 (Thats 10 to the power of minus 3)

Now I believe that makes the question:

9.02 x 0.010 which equals 0.0902

This answer isn't even available as a choice, so I chose the nearest, 0.00902, and was told I was right.

Now its a long time since I was at school but I'm sure Im right?

So whose correct, me or the BBC?

OTT_Buzzard 12:31 04 Jun 2009

Sorry, the BBC is correct - the decimal place moves 3 places to the left.

babybell 12:40 04 Jun 2009

Yeah I agree with that, but I thought that meant:

10.
1.0 (one movement)
0.10 (two movements)
0.010 (three movements)

9.02 x 0.010 = 0.0902

smartpoly 12:44 04 Jun 2009

9.02
0.902 (one movement)
0.0902 (two movements)
0.00902 (three movements)

Picklefactory 12:45 04 Jun 2009

The decimal point moves on the figure the power is acting on, not the '10'

Bring back old money :o)

babybell 12:48 04 Jun 2009

Its all flooding back to me now! I was thinking of the x10-3 as a seperate sum, not as a whole.

Good job I'm not taking that exam for real!

Thanks for the clarification! I knew the BBC were never wrong! :o^

If the values are rounded to the nearest mm then the vertical length could be anything from 5.55cm - 5.65cm. Similarly, the horizontal length could be 10.35cm - 10.45cm.

It asks for the MAXIMUM POSSIBLE area. That is the maximum possible lengths that would round to those figures, i.e. 5.65 x 10.45 = 59.0425

laurie53 20:34 04 Jun 2009

My God! Are you people doing maths when you don't really have to?

Even 60 years on that simply brings back too many painful (in all senses of the word!) memories.

AL47 21:07 04 Jun 2009

forum member is right
0.5 will round to 1
0.49999999999999 recurring will round to 0

OTT_Buzzard 22:22 04 Jun 2009

Depends on the rounding system you are using and what decimal place you use to start the rounding.

On the assumption that the last deciaml place is used and 'round up at 5, round down at less' is used (which in reality is rarely the case for data analysis):

5.6499 x 10.4499 goes to 5.65 x 10.45

i.e. from 5.6499, the last 9 is rounded up to a 0 and the 1 carries, hence making the 3rd DP a 0 and then adding 1 to the 4. Same principal applies to 10.4499.

OTT_Buzzard 22:23 04 Jun 2009

sorry, that should have read the last 9 is rounded up to 10

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