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# GCSE maths help - upper bounds and lower bounds

1. 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.

2. Do you know the upper and lower bound of the radius

Do you know how to work out the area of the circle
3. Find the area using 4.15 which is the lower bound and then find the area using 4.25 which is the upper bound.
4. (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.

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, , and for 'r', use the UB and LB values, to give you the maximum and minimum areas.
5. i think the lb for radius is 4.215cm and the up is 4.225cm
6. oh okay, but it says 3 sig fig
7. (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.
And do it to 3 sig fig.
8. (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
9. (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
10. (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.
11. (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
12. (Original post by American Vampire)
And do it to 3 sig fig.

Write the answers out in full for comparison ... do not round them
13. (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.
14. (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?
15. (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
16. (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?
17. (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.
18. (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.

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
19. (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
I would get my money back

They are the upper and lower bounds of 4.23 ... neither of them round to 4.22
20. 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
That is wrong, both of those bounds are above the original value lol.

It would be 4.225 and 4.215

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