The Question:

Martin thinks of 2 numbers.

The HCF (Highest common factor) of the numbers is 6.

The LCM (Lowest common multiple) of the numbers is 15.

I did the working out of firstly, factors of 15:

1, 15, 3, 5.

Now, at this point I would normally go to see which numbers there have a factor of 6, so you can rule out 3 of the numbers...

1, 3 and 5 as they are lower then 6, thus cannot have a factor of 6.

Now, were left with 15. There is 2 problems here.

1) 15 Is not a multiple of 6 (thus 6 is not a factor of it).

2) We only have 15, yet martin was thinking of 2 numbers.

Slip up by the exam board in question making, or did we miss something horrifically obvious?