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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

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.

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.

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.

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.

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.

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.

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.

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.