Rounding off and Converting?

Question

Hey. If some of you have seen my recent posts you will know that i have been working of the volume of a cylinder. The length was 1.1m and the diamter was 90cm.

From doing the calculations i got the answer 699435 or 0.699435 etc, varies if i convert. In my book the anwer is 0.70m3. Could it be 0.7m3? I was wondering how to i round off the anwer i got from my calculations? From the book i have been learning from i've only used rounding off when given how many decmal places to move, but it doesn't tell me here. Why do i convert it into metres? Is it because metres are larger than centimetres? Please could you give me a guide like answer on to how to anwer these questions in a maths exam.

Also most importantly if i was in an exam i had the exact question could i put 699435m3 etc. as my anwer or has it got to be 0.70m3? Would an examiner whilst marking my paper give me no marks becuase i didn't round off? How do i know when to round off and not to?

Please help. Thank you.

Answer 1

You need to use the appropriate number of significant figures. Your question had two pieces of information, both with two sig figs, thus your answer should have two sig figs.

0.70 m³ is correct.

As for units, you could use either. Just remember that you would only use two sig figs so the answer in cm³ would be 700,000 cm³ (though the number of sig figs would be unclear).

Adding unneeded precision to your answer should get a deduction from a grader. Such precision is meaningless given what wew know about the input data. Answering 0.699435 m³ is incorrect.

Answer 2

well usually rounding off has to be done very precisely.

Any number above the digit 5 is rounded of as 1.

eg. 3.8936 you round the last digit off like - 3.894, just add 1 to the previous no.

So now the no. is - 3.894

For the next no. - 4, you round it off by just simply cancelling it off because it is lesser than 5. i.e - from 3.894 you change it to - 3.89

So now we get - 3.89 now when we round it up we get - 3.9
Answer is 4

But in certain questions they may ask you round it up to two places of decimal or three places of decimal.

In these questions, three places of decimal of the above number would be - 3.893. i.e three places AFTER decimal.

Similarly, two places would be 3.89

For the third part of your question-

It would be best if you rounded up your ans.

You could just say

ans - .699435 m3
OR
.70 m3

You definately should not loose marks this way.

Hope it helped .

Answer 3

wikipedia.com