Year 9 maths homework extension

Hey guys. I finished my regular homework and the teacher has given us 15 extension questions which I can't answer any of. Try them out, I think they are a bit beyond what a year 9 should know...

1. A 3 digit number is 629 times less than the sum of all other three digit numbers. What is this number?

2. 117% of David's mass equals 17% of Goliath's mass. What is the ratio of their masses?

3. Find the smallest possible integer divisible by 45, the sum of whose digits is 45.

4. The number 'a' can be obtained when the digits of the three digit number 'b' are written in the reverse order. If the product 'ab' is equal to 214,875 what are the values of 'a' and 'b'?

7. If a + b = 2 and a^2 + b^2 = 8 what is the value of 1/a + 1/b ?

8. Let a, b and c be distinct non-zero digits such that:

N = (abc)(bca)(cab) + 1 is divisible by 9

What is the smallest value a+b+c can have?

Thats just some, see if you can answer any...