Year 12s: what will be the first way you research your future options? >>

probability at most one event occur?

TSR George

this person has 20 ties

2 red 3 blue 15 mixed colours
he selects 2

find the probability that at most one is red

Spoiler

Reply 1

Zacken

Hint: Does 1 - probability (of something) ring a bell for you?

(edited 8 years ago)

Reply 2

TSR George

Original post by Zacken

Hint: Does 1 - probability (of something) ring a bell for you?

it does but elaborate?

1 - 2/20?? i tend to forget everything after exams :s

Reply 3

Zacken

Find the probability that they are both red. Then 1 - that is the probability that they are not both red, which is the same as saying that either none or one is red which is the same as saying that at most one is red.

Reply 4

TSR George

Original post by Zacken

so 1 - 4/40?

or 1 - 1/10?
i feel so dumb

Reply 5

Zacken

He has twenty ties. He picks two, the probability that the first one is red is 2/20. The probability that the second one is red is 1/19.

The probability that he gets two reds is then 2/20 * 1/19.

Reply 6

TSR George

Original post by Zacken

He has twenty ties. He picks two, the probability that the first one is red is 2/20. The probability that the second one is red is 1/19.

The probability that he gets two reds is then 2/20 * 1/19.