Bounds - Significant Figure

  • 2 votes

i can find the upper n lower bound when they say to the correct decimal point but what about significant figure.. what do you do.. please help me asap.. got my exam on monday..

take this question as an example..

Given that V = 2.18 correct to 3 sigfig and R = 126 correct to 3 sigfig

Calculate the lower bound of the current..

The formula for current is I = V / R


Posted Sat 2nd March, 2013 @ 11:15 by ? Secret - Team GR
Edited by ? Secret - Team GR on Sat 2nd March, 2013 @ 11:15

8 Answers

  • 1 vote

I'm really bad at rounding to sig figs but I think if you have a number like 0.0098 you would start rounding the 98 part of it and miss out the zeros.

So i think the 2.18 answer would be 2.175 (rounded to the lower bound) because the '8' is the 3rd figure in the number.

Hope this helps :)

Answered Sat 2nd March, 2013 @ 11:25 by :) PurpleJaguar (: - Team GR
  • 1 vote

Hiya
No this isn't confusing dont worry; 

I would have thought that 0.90 rounded to 1d.p would be 0.95(upper)? Because; An easy way to work this out is- one decimal place means 0.1, so if we divide 0.1 by 2 we get 0.05 and to find the upper bound you would do 0.90+0.05=0.95 and for the lower you'd do 0.90-0.05=0.85

I think...

If that makes sense?

Hope it helps :)

Answered Sun 3rd March, 2013 @ 14:02 by :) PurpleJaguar (: - Team GR
Edited by :) PurpleJaguar (: - Team GR on Sun 3rd March, 2013 @ 14:05
  • 0 votes

BTW in this question I would do the lower bound of voltage (V) divide by the upper bound of resistance (R) right ???

oh wait here is the exact question..

 http://www.bland.in/GCSE%20Maths/bounds.pdf - q7 - last page (page 8)

Answered Sat 2nd March, 2013 @ 11:18 by ? Secret - Team GR
  • 0 votes

oh okay.. thnx :) PurpleJaguar (:

Answered Sat 2nd March, 2013 @ 12:10 by ? Secret - Team GR
  • 0 votes

Sorry I know I didnt really answer your question properly

Answered Sat 2nd March, 2013 @ 16:30 by :) PurpleJaguar (: - Team GR
  • 0 votes

hey dw.. i kind of get it now.. just prayin it doesn't come up on mondays paper :/

Answered Sat 2nd March, 2013 @ 20:09 by ? Secret - Team GR
Edited by ? Secret - Team GR on Sat 2nd March, 2013 @ 21:13
  • 0 votes

Can I ask something else please..

Basically I was practising bound questions to be more confident.. 

I came across these two questions..

Write down the upper bound and lower bound for 

1) 0.09 ( to 2dp)

2) 0.90 (to 2 dp)

I though the upper and lower bound for question one...

1) 0.09 ( to 2dp) .... is 0.085 (lower) and 0.095 (upper)

2) 0.90 (to 1 dp) ... is 0.895 (lower) and 0.905 (upper)

but the answers in the textbook say this..

1) 0.09 ( to 2dp) .... is 0.895 (lower) and 0.905 (upper)

2) 0.90 (to 1 dp) ... is 0.085 (lower) and 0.095 (upper)

Sorry I know its confusing but do you agree with my answers or the textbook.. if you agree with the text book can you explain how you get the answers.. the more opinions I have from people on this the more it will help.. 

Answered Sat 2nd March, 2013 @ 21:18 by ? Secret - Team GR
  • 0 votes

seriously ur a life saver.. i finally get it.. thank u soo much !!!

your explanation was very helpful :)

Answered Sun 3rd March, 2013 @ 14:54 by ? Secret - Team GR
Edited by ? Secret - Team GR on Sun 3rd March, 2013 @ 15:00