My son is in 4th standard. He needs help on Application of LCM - Lowest Common Multiple and HCF - Highest Common Factor. Any help on this would be very much appreciated.

Regards
Dinesh

LCM (Least Common Multiple) or LCD (Least Common Divisor) is used when you are adding or subtracting fractions. Each denominator must be the same in order to perform that operation.

Example: must be changed to with 12 being the LCM of 3 and 4.

HCF (Highest Common Factor) or GCF (Greatest Common Factor) is used to reduce a fraction to simplest form.

Example: simplifies to by dividing both the numerator and denominator by the HCF of 4.

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He who knows not and knows not that he knows not is a fool, shun him. He who knows not and knows that he knows not is a child, teach him. He who knows and knows not that he knows is asleep, wake him. And he who knows and knows that he knows is wise, follow him.
-- Persian Proverb

Thank you very much.

Would be interested to know if there are more usages/applications of LCM and HCF.

LCM application:

The front wheels of a toy truck are 4 inches in circumference. The back wheels are 7 inches in circumference. If the truck travels in a straight line without slippage, how many inches will the truck have traveled when the front wheels have made 12 more revolutions than the back wheels?

(A) 112 (B) 64 (C) 48 (D) 36 (E) 28

Answer: 112

Answer should be multiples of 4 and 7. so it is 28, 56, 112.....and so on
suppose if we choose 28, 56, and 112 then

4 will take (28/4) or 7 revolution and 7 will take (28/7) or 4 revolutions and the difference is (7 - 4) or 3....but we are looking for difference of 12.

4 will take (56/4) or 14 revolution and 7 will take (56/7) or 8 so the difference is (14-7) or 7...which is not 12.

4 will take (112/4) or 28 and 7 will take (112/7) or 16 and difference is 12 which is the correct.

__________________
He who knows not and knows not that he knows not is a fool, shun him. He who knows not and knows that he knows not is a child, teach him. He who knows and knows not that he knows is asleep, wake him. And he who knows and knows that he knows is wise, follow him.
-- Persian Proverb