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Multiples and Factors - HCF and LCM Applications

Grade 5CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Factors are numbers that divide a given number completely leaving zero remainder. Visually, if you have 1212 tiles, you can arrange them in rectangular grids of 1×121 \times 12, 2×62 \times 6, or 3×43 \times 4; the dimensions 1,2,3,4,61, 2, 3, 4, 6, and 1212 are the factors.

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A multiple is the product of a given number and any whole number. On a number line, multiples of 55 look like equal jumps of 55 units each, landing on the points 5,10,15,20,…5, 10, 15, 20, \dots.

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Prime Factorization involves breaking down a composite number into a product of prime numbers. This is often visualized using a 'Factor Tree' where the number sits at the top and splits into branches until only prime numbers (the 'leaves') remain.

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The Highest Common Factor (HCF) is the largest number that divides two or more numbers exactly. When comparing two sets of factors, you can use a Venn Diagram where common factors are placed in the overlapping center; the largest value in this intersection is the HCF.

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The Lowest Common Multiple (LCM) is the smallest non-zero common multiple of two or more numbers. If you imagine two frogs jumping on a number line, one jumping 44 units and the other 66 units, the LCM (1212) is the first point where both frogs will land.

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HCF is applied in real-life situations where you need to 'split' or 'divide' things into the largest possible equal sections or groups, such as finding the maximum length of a ruler to measure different ropes exactly.

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LCM is applied in real-life situations involving 'repetition' or 'cycles' that happen at different intervals, such as finding when two bells ringing at different times will next chime together.

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The Relationship Rule states that for any two numbers, the product of their HCF and LCM is equal to the product of the two numbers. This can be visualized as a balanced scale: HCF×LCM=Number1×Number2HCF \times LCM = Number_{1} \times Number_{2}.

📐Formulae

HCF×LCM=Product of two numbersHCF \times LCM = Product\ of\ two\ numbers

Product of two numbers=Number1×Number2Product\ of\ two\ numbers = Number_{1} \times Number_{2}

LCM=Product of two numbersHCFLCM = \frac{Product\ of\ two\ numbers}{HCF}

HCF=Product of two numbersLCMHCF = \frac{Product\ of\ two\ numbers}{LCM}

💡Examples

Problem 1:

Two ribbons of lengths 16 m16\ m and 24 m24\ m are to be cut into pieces of equal length. What is the maximum possible length of each piece?

Solution:

  1. To find the maximum equal length, we find the HCF of 1616 and 2424.
  2. Factors of 1616: 1,2,4,8,161, 2, 4, 8, 16
  3. Factors of 2424: 1,2,3,4,6,8,12,241, 2, 3, 4, 6, 8, 12, 24
  4. Common factors are 1,2,4,81, 2, 4, 8.
  5. The highest common factor is 88.
  6. Therefore, the maximum length of each piece is 8 m8\ m.

Explanation:

In problems asking for the 'maximum' size of equal divisions, the HCF (Highest Common Factor) is calculated.

Problem 2:

Two signal lights at different crossings change after every 1010 seconds and 1515 seconds respectively. If they change together at 9:00 AM9:00\ AM, when will they change together again?

Solution:

  1. To find when repeating events coincide, we find the LCM of 1010 and 1515.
  2. Multiples of 1010: 10,20,30,40,50,…10, 20, 30, 40, 50, \dots
  3. Multiples of 1515: 15,30,45,60,…15, 30, 45, 60, \dots
  4. The first common multiple is 3030.
  5. LCM=30LCM = 30 seconds.
  6. They will change together again at 9:00:30 AM9:00:30\ AM.

Explanation:

In problems involving 'how often' or 'when next' things happen together, the LCM (Lowest Common Multiple) is used to find the next point of coincidence.