I am a bit confused right now but I think this is the explanation.
Knowing the divisibility rule for 10 helps you make a factor tree for any multiple of 10. Why?
- any number that is a multiple of a number is always divisible by the number.
- any multiple of 10, say 50 or 130 or 270 is always divisible by 10!
- since the multiples of 10 is divisible by 10, then it is divisible by the numbers that 10 are divisible by.
Since 60 is a multiple of 10, and 10 is divisible by 5, then 60 is divisible by 5. Since 10 is also divisible by 2, then 60 is also divisible by 2.
It will be easy to make a factor tree because you will know what to put next knowing that the number next is always divisible by the given number.
For example, 70 ( oooh! a multiple of 10, 10 is divisible by 5, so I can put 5 next)
So, I can just divide 70 by 5 and bingo! 14 is its partner and so on.
Now, we have completed our factor tree, it is made easy because of our knowledge that since 70 is a multiple of 10 which the latter is divisible by 5 then we can conclude that 70 is divisible by 5, and therefore, we can put it next.