Maths question

Discussion in 'Sappers' started by devilish, Sep 2, 2009.

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  1. My daughter has just started high school and has come home with this question, amongst others.

    "A large circular pane of glass has a perimeter of 219.8cm, calculate the area of the glass"?

    Now it's been 25 years since I needed to use pi(stop laughing at the back).

    To get the radius I need to divide the perimeter(circumference) by pi and then divide the diameter by 2, correct?

    Then calculate the area by using the pi x r2(pi x radius x radius) correct?

    I get an answer of- area = 3846.5.

    According to my daughters friends rather stuck up school teacher mother, it's wrong.

    Is it, I'd dearly love to tell her she was in fact wrong.

    Sorry for boring you's but it's bugging me.
  2. 3844.55076
  3. A large circular pane of glass has a perimeter of 219.8cm,

    what is that in old money
  4. thats what i make it! Editted to add 'eod'
  5. The method's right but you must have typed it into the calculator wrong or something.

    Answer 2 is also slightly off (rounding errors? 3.14 used for pi?)

    Remember not to quote too many decimal places or significant figures!
  6. Deleted. !
  7. 3844.55 to 2dp

    Circumference is 2 x pi x r. r = 34.98225649 ^2 = 1223.758269

    Area = pi x r^2 = 3844.549988
  8. Perimeter = pi x D = 2 x pi x r
    > 219.8 = 2 x pi x r
    > r = 219.8 / (2 x pi) = 34.98cm
    > Area = pi x r x r = pi x 34.98 x 34.98 = 3844.5 sq cm
  9. now you are just showing off and no one likes a smart alec
  10. agreed
  11. 3844.541 - using 3.1416 as pi.

    3844.05 if you use 3.142 as pi.
  12. Maybe it's this calculator or me but when I divide 219.8 by pi(3.14) I get 70?
  13. It's right. Then 3846.5.

    It depends on how many places you are taking pi too.

    I suggest you get her sorted.