I think he's talking about SATs or a similar type of test... I was talking about standardized tests in general, the SAT in specific since it's the closest thing I've taken.
As far as decimal numbers; ignore the decimal, multiply like two larger normal numbers, then put the decimal in so that the total number (including any 0's you had to write) of digits to the right 'on top' are also on 'the bottom'.
Fractions... well there it pays to know a lot about factoring and primes (for reducing and for finding lowest common denominator). However most things can be brute forced and then reduced later, you just work with larger address spaces. Not really too much of an issue on normal paper, or for normally small, sane, numbers in more complex digital systems... however that's getting beyond your scope. Oh, and usually for trivial things 'floating point' numbers are faster and easier to work with. (I say trivial, because they are always approximations, usually good enough that it doesn't matter, but it's easy to make mistakes with them that amplify the loss of precision.)