A bag contains 12 discs

7 are red

3 are blue

2 are yellow

Two discs are taken from the bag at random, without replacement. Work out the probability that the two discs are the same colour. Please help :)

If they are both red, 7/22

If both blue, 1/22

Yellow, 1/66

Step-by-step explanation:

7/12 times 6/11 (both decrease by one because there is no replacement)

3/12 times 2/11

2/12 times 1/11

hello from mrbilldoesmath!

answer:

a(n) - a(n-1) -3

discussion:

this ones a bit interesting. given a(n) = 5 - 3n consider this:

a(n-1) = 5 - 3(n-1)

          = (5 - 3n) + 3             => but a(n) = 5 - 3n, the first term

          = a(n)   + 3                 => subtract 3 from both sides

a(n-1) -3 = a(n)  

or

a(n) - a(n-1) -3

you,

mrb

she gotta workk that a 2

step-by-step explanation: