The Student Room Group
Competition - post a photo you've taken of nature >>
Competition - post a photo you've taken of nature >>
Competition - post a photo you've taken of nature >>

GCSE maths help - upper bounds and lower bounds

the radius of a circle is 4.22cm, to three significant figures.

a) find the lower bound and upper bound for the area of the circle
b) hence give the area of the circle to as many significant figures as can be justified.

thanks for your help <3

Scroll to see replies

Reply 1
Avatar for TenOfThem
TenOfThem
18
Do you know the upper and lower bound of the radius

Do you know how to work out the area of the circle
Find the area using 4.15 which is the lower bound and then find the area using 4.25 which is the upper bound.
Original post by kitty1011
the radius of a circle is 4.22cm, to three significant figures.

a) find the lower bound and upper bound for the area of the circle
b) hence give the area of the circle to as many significant figures as can be justified.

thanks for your help <3


a) Work out the upper and lower bounds to 1 sf more.

For example, the UB and LB for 5.931 would be 5.9315 and 5.9305.

b) Then use the formula, A=πr2A = \pi r^2, and for 'r', use the UB and LB values, to give you the maximum and minimum areas.
Reply 4
Avatar for kitty1011
kitty1011
OP
i think the lb for radius is 4.215cm and the up is 4.225cm
Reply 5
Avatar for kitty1011
kitty1011
OP
oh okay, but it says 3 sig fig
Original post by TenOfThem
Do you know the upper and lower bound of the radius

Do you know how to work out the area of the circle


a) Upper = 4.225cm and Lower = 4.215cm
Then just work out the area. :biggrin:
And do it to 3 sig fig.
Reply 7
Avatar for TenOfThem
TenOfThem
18
Original post by EatRainbows
Find the area using 4.15 which is the lower bound and then find the area using 4.25 which is the upper bound.


These are incorrect
Reply 8
Avatar for TenOfThem
TenOfThem
18
Original post by kitty1011
i think the lb for radius is 4.215cm and the up is 4.225cm


Yep use these to work out the area

Then you can compare the answers
Original post by kitty1011
oh okay, but it says 3 sig fig


It says that the rounding is 3 sig fig, so that tells you the upper and lower bounds.
Original post by American Vampire
It says that the rounding is 3 sig fig, so that tells you the upper and lower bounds.


She knows the bounds
Original post by American Vampire

And do it to 3 sig fig.




Write the answers out in full for comparison ... do not round them
Original post by TenOfThem
She knows the bounds


She asked why the first part was in 3 sig figs, when the bounds had 4 digits.
Original post by TenOfThem
Write the answers out in full for comparison ... do not round them


Read the second part. As many sig figs as appropriate. 3 are used in the question, so do it to 3 significant figures. Cool?
Original post by American Vampire
She asked why the first part was in 3 sig figs, when the bounds had 4 digits.


I think she was replying to the poster who gave the incorrect bounds as the OP had already given the correct bounds
Original post by American Vampire
Read the second part. As many sig figs as appropriate. 3 are used in the question, so do it to 3 significant figures. Cool?


No, not cool

the OP needs to look at the answers and compare them

She will then see how many sig fig gives the same answers .... that is how she will answer the second part

cool?
Original post by TenOfThem
No, not cool

the OP needs to look at the answers and compare them

She will then see how many sig fig gives the same answers .... that is how she will answer the second part

cool?


I know that, but I would say that 3 sig figs is appropriate anyway.
Original post by kitty1011
the radius of a circle is 4.22cm, to three significant figures.

a) find the lower bound and upper bound for the area of the circle
b) hence give the area of the circle to as many significant figures as can be justified.

thanks for your help <3


from what i learnt i think the upper bound is 4.235 and the lower is 4.225 thats the way i got taught sorry if im wrong though :s-smilie::confused:
Original post by sheepstick
from what i learnt i think the upper bound is 4.235 and the lower is 4.225 thats the way i got taught sorry if im wrong though :s-smilie::confused:


I would get my money back :smile:

They are the upper and lower bounds of 4.23 ... neither of them round to 4.22
haha does anyone else think.....oh GREAT when an easy GCSE question comes up like this. I can finally help!


Original post by sheepstick
from what i learnt i think the upper bound is 4.235 and the lower is 4.225 thats the way i got taught sorry if im wrong though :s-smilie::confused:


That is wrong, both of those bounds are above the original value lol.

It would be 4.225 and 4.215

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you