Hi, im trying to solve a question on a past paper; here is one that is very similar to it- New Page 1
Im presuming the probability of blue marbles is 7/(k+7)
On part (d) would i have to do something like:
7/(k+7) x k/(k+7) = 4/9 ?
Ive tried the above equation but it doesnt seem to work out seeing as it doesnt give me any square numbers as the LCM becomes 9(k+7)
any help would be much appreciated.
Originally Posted by david18
you nearly did it ...
k + 7 k + 7
describes the probability for one colour. In your problem the colour isn't mentioned so you get the same probability for the second colour too. Therefore your equation must be:
7 k 7·k
⎯⎯⎯⎯⎯·⎯⎯⎯⎯⎯ = ⎯⎯⎯⎯⎯⎯⎯⎯
k + 7 k + 7 2
(k + 7)
Solve for k and you'll get:
⎯⎯⎯⎯⎯⎯⎯⎯·2 = ⎯
(k + 7)
These are the solutions of the equation
k = ⎯ ∨ k = 14
Expand the brackets and multiply by 2 and you'll get the given result.
⎜k - ⎯⎟·(k - 14) = 0