Topic Details (Notes format)

How to Calculate Combinations (Unordered Selections)

Subject: Mathematics

Book: Maths Mastery

Combinations focus on ways to choose k items out of n without regard to order, calculated as C(n, k) = n! / [k!(n–k)!]. For instance, to find the number of ways to select 2 fruits from {Apple, Banana, Cherry}, you have 3 choices: AB, AC, BC, which is C(3, 2) = 3. Combinations appear in scenarios like forming committees, picking lottery numbers, or combining flavors in recipes. Understanding the difference between permutations and combinations clarifies everything from business inventory groupings to advanced probability, ensuring a robust combinatorial foundation.

Practice Questions

If x - y = 5 and x + y = 15, what is the value of x?

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What is the sum of all even numbers between 1 and 50?

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What is the HCF of 48 and 180?

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If a number is divisible by 9, it is also divisible by which of the following?

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If 2x = 16, what is the value of x?

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If the ratio of two numbers is 3:5 and their HCF is 4, what are the numbers?

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What is the probability of drawing an ace from a standard deck of 52 cards?

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The perimeter of a rectangle is 50 cm, and its length is 15 cm. What is its width?

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A number is increased by 20% and then decreased by 20%. What is the net change?

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If x^2 - 6x + 9 = 0, what is the value of x?

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