Use simultaneous equations with variable a and d.
Then when you solve for a and d just find the sum when n=20
i.e.
a+5d=23
a=23-5d (1)
10/2(2a+9d)=210 (2)
sub (1) in (2)
Solve.
Re: 2012 Year 9 &10 Mathematics Marathon
That's true. Some people read solutions and think they understand, but when you give them a similar question, they have no idea.
Re: 2012 Year 9 &10 Mathematics Marathon
A mushroom farmer has sent an order of 70 kg of mushrooms to the markets in standard cases. If he had used larger cases, each capable of holding 2 kg more, he would have used 4 fewer cases.
What is the capacity (in kg) of the standard case?
Re: 2012 Year 9 &10 Mathematics Marathon
It's called LaTeX. http://www.codecogs.com/latex/eqneditor.php <you can try it out here
To post with it on here [ TEX ] *put code in here* [ / TEX ] without any spaces in the brackets.
You'll~get~used~to~it
Re: 2012 Year 9 &10 Mathematics Marathon
Another thing you should keep in mind is that the side length of an equilateral triangle inscribed in a circle of radius R is R\sqrt3. This can be proved later with calculus. So in this case, R*sqrt3=1, therefore R=1/sqrt3 (0.577...)
Just an...