but why must we find the lcm of 8,12,42,63 and 108 ?

Because from the explanation, the number of flowers is divisible by 8,12,42,63,108, to give you a whole number result.

This means that it is a common multiple of all 5 of those numbers.

Since the minimum number of yellow flowers implies the minimum of total number of flowers possible,

Finding the LCM of these 5 numbers would give you your required minimum total number of flowers.


Recall that LCM is Lowest Common Multiple.

If you look at Lim's working, he found the LCM of 42,63 and 108 first.

He then found the LCM of 3,8,12.

He then took these two results and found their LCM.

The final result 1512 is a number , which is the lowest possible one that is divisible by all 6 numbers.


He did it in 3 separate steps while mine was a combination of all 3. I basically found the LCM of the 5 numbers straight away.

I didn't have to add 3 inside when I do the LCM since 4 out of the 5 numbers contained prime factor 3. This implies my LCM would have at least one factor 3 inside.