CLASS 6 MATHS · PLAYING WITH NUMBERS

HCF and LCM

HCF is the biggest number dividing both. LCM is the smallest number both divide into.

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Worked examples

Example 1 · level 1

Find the HCF of 6 and 9.

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6 = 2 × 3
9 = 3 × 3
HCF = 3.

Answer: 3

Example 2 · level 2

Find the HCF of 15 and 25.

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15 = 3 × 5
25 = 5 × 5
HCF = 5.

Answer: 5

Example 3 · level 3

Two ribbons are 22 cm and 33 cm long. They must be cut into pieces of the same length with nothing left over. What is the longest possible piece (in cm)?

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22 = 2 × 11, 33 = 3 × 11.
Common factors multiply to 11.
Longest piece = 11 cm.

Answer: 11 cm