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Maths Olympiad – LCM and GCD

Posted on: November 5, 2015

Today we are going to learn Least Common Multiple and Greatest Common Divisor/Factor.

LCMGCD

Power Point:

PDF Worksheet: MathsOlympiad-Intermediate-L14-LCM-and-GCD.pdf

Here is a question I encountered recently which uses LCM to solve.

HelpQuestion

And here is the explanation:

Since when Wendy jumps 3 or 5 steps, the start and end tiles coincide, the concept here is really Least Common Multiple.

LCM of 3 and 5 is 15. At 2 more tiles at the end (One she stopped at, which is the second last tile, and one for the last tile).

In fact, 17, 17 + 30, 17 + 45, 17 + 60, … all will meet the above requirements. So the least is 17.

p.s Thanks Raymond Ng

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