Math PicnicEvery sheet is a promise

Complementary events, step by step

Every event has a complement — the chance it does NOT happen — and the two always add to one whole.

Practice Practice sheetNew questions
The question

2 red, 6 blue, 4 green — P(not red)

2 + 6 + 4=12
2 + 6 + 4=12
red:2
not red:12 − 2 =10
2 + 6 + 4=12
not red:10
+=
which is1
2 + 6 + 4=12
=
  1. Count EVERYTHING first, before the ones being asked about: 2 + 6 + 4 = 12 altogether. That is the bottom of the fraction, and it is the half that gets swapped for the wrong number.
  2. Read the question again: it asks for NOT red. So the wins are everything ELSE in the bag — all 12 of them except the 2 red, which is 12 − 2 = 10.
  3. Chance is the wins OVER the total — not over the rest. So it is 10 out of 12.
  4. Check it: the chance of red and the chance of not red have to fill the bag between them. 2 out of 12 and 10 out of 12 make 12 out of 12 — the whole bag, which is 1. If they do not add up, one of the two counts is wrong.
  5. And 10/12 can be written in bigger pieces: 5/6.

How it works.

  1. 01

    Count EVERYTHING first, before the ones being asked about: 2 + 6 + 4 = 12 altogether. That is the bottom of the fraction, and it is the half that gets swapped for the wrong number.

  2. 02

    Read the question again: it asks for NOT red. So the wins are everything ELSE in the bag — all 12 of them except the 2 red, which is 12 − 2 = 10.

  3. 03

    Chance is the wins OVER the total — not over the rest. So it is 10 out of 12.

  4. 04

    Check it: the chance of red and the chance of not red have to fill the bag between them. 2 out of 12 and 10 out of 12 make 12 out of 12 — the whole bag, which is 1. If they do not add up, one of the two counts is wrong.

  5. 05

    And 10/12 can be written in bigger pieces: 5/6.

Pick another skill