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probability question

20 counters in a bag
8 are yellow
12 are green
asif takes 2 counters out of the bag
work out probability they the two are different colours
(non calc)

i did some of the tree stuff and ending up getting ( 2/5 x 12/19 ) + ( 3/5 x 8/19 ) not to sure how i can do that without a calculator? and im not to sure thats right either
Original post by Gent2324
20 counters in a bag
8 are yellow
12 are green
asif takes 2 counters out of the bag
work out probability they the two are different colours
(non calc)

i did some of the tree stuff and ending up getting ( 2/5 x 12/19 ) + ( 3/5 x 8/19 ) not to sure how i can do that without a calculator? and im not to sure thats right either


It's correct.

Combine the fractions - they have the same denominators - and reduce your answer to lowest terms, leaving it as a fraction.
Original post by ghostwalker
It's correct.

Combine the fractions - they have the same denominators - and reduce your answer to lowest terms, leaving it as a fraction.

i see they have the same denominators, how do i combine them though?
Original post by Gent2324
20 counters in a bag
8 are yellow
12 are green
asif takes 2 counters out of the bag
work out probability they the two are different colours
(non calc)

i did some of the tree stuff and ending up getting ( 2/5 x 12/19 ) + ( 3/5 x 8/19 ) not to sure how i can do that without a calculator? and im not to sure thats right either

Im so confused where does 5 come from?
Original post by JayJayGold
Im so confused where does 5 come from?


8/20 and 12/20 simplified
Original post by Gent2324
i see they have the same denominators, how do i combine them though?


25×1219+35×819=2×12+3×85×19\displaystyle \frac{2}{5}\times \frac{12}{19}+\frac{3}{5}\times \frac{8}{19}=\frac{2\times 12 + 3\times 8}{5\times 19}
Original post by Gent2324
i see they have the same denominators, how do i combine them though?


( 2/5 x 12/19 ) + ( 3/5 x 8/19 ) = ( 24/95 ) + ( 24/95 ) = ( 48 / 95 )

This is already in it's simplest form so you don't need to simplify anything :smile:
Original post by Gent2324
20 counters in a bag
8 are yellow
12 are green
asif takes 2 counters out of the bag
work out probability they the two are different colours
(non calc)

i did some of the tree stuff and ending up getting ( 2/5 x 12/19 ) + ( 3/5 x 8/19 ) not to sure how i can do that without a calculator? and im not to sure thats right either


Sadly tree diagrams are on non- calculator papers

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