and subtraction, go left to right; ditto with multiplication and division. Here’s a
handy-dandy graphic for you to tattoo on your forearm:
More helpfully, it should be PREMDAS because we shouldn’t forget “R” for
roots. Operations under root signs should be done at the same time as the
exponents (move from left to right to decide which to do first). PREMDAS is
precisely the kind of math concept you learned ages ago and think you know, but
being hazy on this can really mess you up.
If you go from left to right, you get 40. If you follow PREMDAS, you get 15.
Those are two different answers. The first is wrong, the second is right. The SAT
will try to catch you on this.
A root is really just a type of exponent. That’s why the “R” is often left out.
—Samantha
MENTAL MATH TRICK 3: DIVIDING TRICKS
Division is one of the more annoying operations to do in your head. A few SAT
problems will require that you determine whether a large number is divisible.
For example, do you know if 32,571 is prime? To solve this, you could do a
whole bunch of trial and error with your calculator. But this will take a while,
and if no calculator is allowed, you’re in trouble. So consider this chart a list of
cheat codes to help you determine whether a large number is divisible, and by
which numbers.
IT’S
DIVISIBLE
BY IF EXAMPLE1 It is an integer. Do you really need
one?2 It’s an even number. Hmm . . .