Math Is Fun Forum

Karn

Member

Registered: 2009-11-15

Posts: 14

Number: Scientific notation, significant figures and so on

Hi Everyone!

Q.1) To the nearest square centimetre a solid cube has a total surface area of 1090 cm^2
           
a) Determine the length of each of the cubes edges giving your answer in millmetres, to the nearest millimetre         
b) Determine the volume of the cube giving your answer to the nearest  10cm^3

Q.2) Australia has a land area of approximately 7.68 X 10^6 square kilometres and a population of approximately 20 million.

a)    How many square kilometres is that for each person?
b)    How many people is that for each square kilometre?

And finally

Q.3) Evaluate each of the following giving your answers in scientific notation and correct to 3 significant figures.

a) (7.48 X 10^3)  X (6.34 X 10^6)

For this one I got…

4.74 X 10^9 (which is of course is incorrect however how do solve this without a calculator)

I thought when you multiply numbers with powers you add the powers together but  with this one instead of 10^9 by adding 3 and 6 the correct answer is 4.74 X 10^10
Please explain.

Thank you very much for any help.

Last edited by Karn (2010-02-01 23:19:39)

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Number: Scientific notation, significant figures and so on

Hi Karn

I thought when you multiply numbers with powers you add the powers together but  with this one instead of 10^9 by adding 3 and 6 the correct answer is 4.74 X 10^10
Please explain.

You do add powers but you are forgetting about the mantissa.

7.48*6.34 = 47.4232 Do you see it now?

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.