No, some numbers, eg sqrt 2, are irrational, which means they cannot be written as a ratio between two whole numbers. Some numbers are also transcendental, but you don't want to go there!
No.
Most can - simply by writing the decimal above ten to the power of however many decimal places there are.
0.3456789 can be written as 3456789/10000000
But some decimals are endless - such as...
How would you show that every positive integer can be written as the product of a power of 2 and an odd?.
If P is a positive integer, then let 2n be the largest power of two that divides P.
Then P =...