gmattesttaker556 wrote:

Hi, quick question on the treatment of the use of the words "difference between" on GMAT--I have two sources that provide varied information:

In the GMAT Club Quant book it says "Difference between x and y" implies "x-y"

In the problem that follows here gmatclub.c0m/forum/abe-beth-carl-and-duncan-are-four-siblings-among-which-abe-and-carl-196028.html (cant post URLs yet b/c new member + kudos...change 0 to an 0 in .c0m); difference between is assumed to represent either way of subtraction as per atom's and eGmats responses and the accepted OA.

I am very very confused as to which to follow and would appreciate any clarity.

Thanks

Dear

gmattesttaker556,

I'm happy to respond.

I would say that in the phrasing "

difference between X and Y," there's no generally-agreed-upon mathematical rule for translating those particular words into algebra. It's unambiguously clear that subtraction is implied, but whether the difference must be positive and whether we are subtracting in one order or another is unclear. My gut sense is that this typically would mean

|X - Y|, the number-line separation between the two quantities. For example, look at the

problem you cited.

I. The difference between Beth’s age and Abe’s age is a prime number.A prime number, by definition, is a kind of positive integer, so we know the difference must be positive. Since the prompt tells us that

B > A, then this difference is

(B - A). I would say that any bonafide Quant problem would not leave us hanging on this point. If it says "

difference between ___ and ___," something else in the problem will make obvious which way the subtraction should go.

Does all this make sense?

Mike

_________________

Mike McGarry

Magoosh Test Prep

Education is not the filling of a pail, but the lighting of a fire. — William Butler Yeats (1865 – 1939)