Which factors are not included in the prime factorisation of a composite number?

Which of the following statements are true?

(a) If a number is divisible by 3, it must be divisible by 9.

(b) If a number isd divisible by 9, it must be divisible by 3.

(c) A number is divisible by 18, if it is divisible by both 3 and 6.

(d) If a number is divisible by 9 and 10 both, then it must be divisible by 90.

(e) If two numbers are co-prime, at least one of them must be prime.

(f) All numbers which are divisible by 4 must also be divisible by 8.

(g) All numbers which are divisible by 8 must also be divisible by 4.

(h) If a number exactly divides two numbers separately, it must exactly divide their su,

(i) If a number exactly divides the sum of two numbers, it must exactly divide the two numbers separately.

Here are two different factor trees for 60. Write the missing numbers.

(a)

(b)

Write the greatest 4-digit number and express it in terms of its prime factorsd.

Write the smallest 5-digit number and express it in the form of its prime factors.