Yes, since 10 is divisible by 5. Likewise, every number which is divisible by 9 is also divisible by 3.
Yes, since 10 is divisible by 5, ALL numbers that are divisble by 10 are also divisble by 5.
Not all of them, if you flipped the question around to ask area numbers divisible by 10 also divisible by 5? then the answer would be yes. The answer is no.
No - but all the numbers divisible by 10 are divisible by 5 !
because 10 is also divisible by 2 and 5.