6. Explain why 7 × 11 × 13 + 13 and 7 × 6 × 5 × 4 × 3 × 2 × 1 + 5 are composite numbers.
6. Explain why the following numbers are composite:
(i) 7 × 11 × 13 + 13
= 13 (7 × 11 + 1)
= 13 × 78
Since it has factors other than 1 and itself, it is a composite number.
(ii) 7 × 6 × 5 × 4 × 3 × 2 × 1 + 5
= 5 (7 × 6 × 4 × 3 × 2 × 1 + 1)
Since it is divisible by 5, it has factors other than 1 and itself.
Hence, the given number is a composite number.