Math Problem Statement

Un sac contient six boules noires, deux boules blanches et quatre boules rouges. On tire au hasard simultanément trois boules du sac. Combien y a-t-il de tirages possibles ? Combien de tirages sont constitués de trois boules de couleurs différentes ? Combien de tirages sont constitués de trois boules de la même couleur ?

Solution

Let us break this problem into steps and solve each part systematically:

Given Information:

  • 6 black balls, 2 white balls, and 4 red balls.
  • Total balls = 6+2+4=126 + 2 + 4 = 12.

We are drawing 3 balls simultaneously.


a) How many total draws are possible?

The total number of ways to choose 3 balls from 12 is given by the combination formula: (nk)=n!k!(nk)!\binom{n}{k} = \frac{n!}{k!(n-k)!}

Here n=12n = 12 and k=3k = 3: (123)=12×11×103×2×1=220\binom{12}{3} = \frac{12 \times 11 \times 10}{3 \times 2 \times 1} = 220

Thus, 220 total draws are possible.


b) How many draws consist of balls of three different colors?

To have balls of three different colors, we must select:

  • 1 black ball,
  • 1 white ball,
  • 1 red ball.

The number of ways to select 1 ball of each color is: (61)×(21)×(41)\binom{6}{1} \times \binom{2}{1} \times \binom{4}{1}

Calculating each term: (61)=6,(21)=2,(41)=4\binom{6}{1} = 6, \quad \binom{2}{1} = 2, \quad \binom{4}{1} = 4

So: 6×2×4=486 \times 2 \times 4 = 48

Thus, 48 draws consist of balls of three different colors.


c) How many draws consist of balls of the same color?

To have all 3 balls of the same color, they must all be:

  1. Black balls, or
  2. White balls, or
  3. Red balls.

The number of ways to choose 3 balls of the same color is:

  • For black balls: (63)\binom{6}{3},
  • For white balls: (23)\binom{2}{3} (not possible as there are only 2 white balls),
  • For red balls: (43)\binom{4}{3}.

Calculating each term: (63)=6×5×43×2×1=20,(23)=0,(43)=4×3×23×2×1=4\binom{6}{3} = \frac{6 \times 5 \times 4}{3 \times 2 \times 1} = 20, \quad \binom{2}{3} = 0, \quad \binom{4}{3} = \frac{4 \times 3 \times 2}{3 \times 2 \times 1} = 4

Adding these: 20+0+4=2420 + 0 + 4 = 24

Thus, 24 draws consist of balls of the same color.


Final Answers:

a) Total draws possible: 220
b) Draws with three different colors: 48
c) Draws with balls of the same color: 24

Would you like a detailed explanation of any step or further assistance?


5 Related Questions:

  1. How would the results change if we drew 4 balls instead of 3?
  2. What is the probability of getting exactly two red balls in a draw of 3?
  3. How many ways can you draw 2 balls of the same color and 1 of a different color?
  4. What is the probability of drawing no black balls in a single draw of 3?
  5. How many different distributions are possible if 4 balls are drawn at once?

Tip:

When solving combinatorics problems, always verify whether repetition is allowed (permutations vs. combinations) to avoid calculation errors.

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Math Problem Analysis

Mathematical Concepts

Combinatorics
Counting Principles

Formulas

Combination formula: C(n, k) = n! / [k!(n-k)!]

Theorems

Basic Counting Principle

Suitable Grade Level

Grades 9-12