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In group A there are 7 boys and 3 girls In group B there are 2 boys and 8 girls If two people are selected at random from either of group A and B, find the probability that both are boys. Answer is 11/45... I keep getting 22/45 :( Thanks

I had 4 people in our 3U maths class including myself. lol. Other classes had around 10-14.

sorry yes, orbital velocity is indeed 2pi r / t I got confused with angular velocity :S

For the same planet r^3/T^2 is a constant. Orbital velocity = \frac{2 \pi r}{T}=\sqrt{\frac{GM}{r}} Must use SI units. NB: Escape velocity = \sqrt{\frac{2GM}{r}}

Oh come on.... :p It's a method commonly employed and it never matters if u take negative or positive since you end up squaring the expression to make it a polynomial.

But Jetblack I recall your teacher took marks off for something like not putting +/- for finding a polynomial equation with roots a^2, b^2 and c^2 (where a, b and c are roots of the original polynomial equation). That's also stupid IMO.

Just the sum of all infinitely small slices, isn't it?

Hi... I love ur siggy :D

I suck at this topic :( Consider a pack of 50 playing cards consisting of 5 colours Red, Blue, Green, Yellow and Orange, with cards numbered from 1 to 10 for each colour. (a) If six cards are dealt at random from the pack find the number of ways of obtaining four 9's and two eights. (b) If...

Yeah he said to us "If you don't want to turn out like me then do something better" (or words to that effect) :P But he is a really good Physics teacher (ie. knows what he's actually on about, unlike most).

Yeah point symmetry, same thing. Usually the geometric approach is easier anyway for most questions (like in Conics).

Okay... The property of an odd function is that it has point symmetry about the origin. I guess you could almost treat this as a 'definition'... Thus it must pass through (0, 0)... BTW, I see how it works now. I didn't see the algebraic approach before. Both approaches are good I guess, but I...

I don't think that is a substainial proof. You need to explain why f(0)=0

(a) From the property of an odd function, odd functions have point symmetry about the origin, ie. Odd functions pass through (0, 0), thus at x=0 f(0)=0. (b) Using the factor theorem, if P(x) is divisible by x, then P(0)=0, which is true using (a) if P(x) is odd.

and integration.

Those formulas used to be in the old 2 unit course, so I guess I wouldn't hurt memorising them.

w=\frac{z-1}{z} \\ wz=z-1 \\ z(w-1)=-1 \\ z=\frac{1}{1-w} \\ |z|=\frac{1}{|1-w|} \\ \text{Since } |z|=2 \\ 2=\frac{1}{|1-w|} \\ \text{ie } |w-1|=\frac{1}{2} \text{ is the locus of w}

That is being systematic. My Physics teacher did the same too without using a textbook :D

It takes John about 5 hours to paint a house. It takes Bob about 3 hours to paint the same house. About how long will it take to paint the house if both of them work together?

Joanne and Sophie went shopping in New York and found a dress shop they loved. They both appreciated the Black Rhinestone Sleeve dress and the Black Bubble dress so much they had to have several of each, but they bought different numbers of each. Joanne bought two Black Bubble and four Black...