significant figure

How to I put a long decimal number into significant figures. A lot of questions ask for three significant figures but I always get the answer wrong even if my answer is correct.

Reply 1

Matrix123

Original post by Emily_L_Murray

How to I put a long decimal number into significant figures. A lot of questions ask for three significant figures but I always get the answer wrong even if my answer is correct.

Can you give an example?
So, if you had to round 0.0000304572 to 3SF, what answer would you give?

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Reply 2

Emily_L_Murray

Would that be 0.0000305000

Reply 3

Matrix123

Original post by Emily_L_Murray

Would that be 0.0000305000

Yup. I don't see where you could have gone wrong. Could you give me an example of one you've done right buy supposedly done wrong? It could just be the mark scheme that's wrong.

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Reply 4

Kevin De Bruyne

Original post by Emily_L_Murray

How to I put a long decimal number into significant figures. A lot of questions ask for three significant figures but I always get the answer wrong even if my answer is correct.

Perhaps you would benefit from finding the section in your textbook for finding values to ...significant places or maybe using bbc bitesize if there is a page on it. Practice makes perfect!

Reply 5

Student403

Original post by Emily_L_Murray

Would that be 0.0000305000

Original post by Matrix123

That's incorrect. it's just 0.0000305

Forget writing any figures after it.

Reply 6

Matrix123

Original post by Student403

That's incorrect. it's just 0.0000305

Forget writing any figures after it.

Oh right, thanks for correcting that :colondollar:

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Reply 7

Rather_Cynical

Significant figures is about the information you have, and the uncertainty.

There is no information about the size of 0.0000304572 before the three, because it's just a series of zeros. It can't tell you when it stops, until you see a non-zero number.

Once you have your first three (or any other non-zero number for that matter), you know the rough size. That's where your significant figures start - your first non-zero number.

The number of significant figures is just counting the number of figures from the first non-zero. If you have three significant figures, it would be 0.0000305 as the fourth significant figure is 5 or greater (so it rounds up)

The reason why you're asked to do this is because in a lot of calculations, you get a massive string of numbers in your calculations but your uncertainty is much bigger so you have to truance your numbers a bit.

The same is true if you're measuring something with a ruler, you can't measure more precisely than to the nearest 0.1cm unless you use a ruler with smaller graduations but your calculations might spit up something like 5.6666666666666cm if you divide by three.