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Need to know area of a circle?
Posted: Wed Aug 07, 2013 6:04 pm
by silverysea
For superselective, do they need to be able to calculate the area of a circle? Tutor did this today but I've not seen it in any test papers tried so far.
Re: Need to know area of a circle?
Posted: Fri Aug 09, 2013 9:47 am
by leanmeamum
they give the formula for the area of a circle or the area, if there is a question involving it.
Maybe the tutor covered the topic just to show how it works so it is easy for the child
to see understand circles
Re: Need to know area of a circle?
Posted: Fri Aug 09, 2013 9:56 am
by silverysea
Ok that does help! It's all about familiarity I guess!
Re: Need to know area of a circle?
Posted: Mon Aug 12, 2013 11:48 am
by parent2013
The answer unfortunately is "Yes" for superselectives. I have seen numerous examples in private school papers from previous years where this concept has been tested. It is not rocket science and there are only 2 formulas to remember.
Circumference : 2 X Pi X Radius (where Pi is 3.14 or 3 for approximation)
OR Pi X Diameter (as Diameter is twice the radius)
Area: Pi X (square of radius)
One example I remember from top of the head is:
1. Ben has a bicycle with a wheel of radius 1m, how much distance it covers in 10 turns
Using Pi = 3, the distance in one turn is the circumference i.e. 2 X 3 X 1 = 6m. Therefore in 10 turns, it will cover a distance of 10 X 6m i.e. 60m.
2. His grandfather "John" has a bicycle with a bigger wheel of radius 1.5m, how much additional distance it covers in 10 turns?
Using Pi = 3, the distance in one turn is the circumference i.e. 2 X 3 X 1.5 = 9m. Therefore in 10 turns, it will cover a distance of 10 X 6m i.e. 90m. The answer is "additional" distance i.e. 90-60 = 30m.