Cracking The SAT Premium

Let’s try another example.

20.A    watch   loses   x   minutes every   y   hours.  At  this    rate,   how many    hours   will    the watch   lose

in  one week?

A) 7 xy

B)

C)

D)

Here’s How to Crack It

This is an extremely difficult problem for students who try to solve it using math-class algebra. You’ll be
able to find the answer easily, though, if you plug in carefully.

What numbers should you plug in? As always, you can plug in anything. However, if you think just a little
bit before choosing the numbers, you can make the problem easier to understand. There are three units of
time—minutes, hours, and weeks—and that’s a big part of the reason this problem is hard to understand. If
you choose units of time that are easy to think about, you’ll make the problem easier to handle.

Start by choosing a value for x, which represents the number of minutes that the watch loses. You might be
tempted to choose x = 60 and that would make the math pretty easy. However, it’s usually not a good idea
to choose a conversion factor such as 60, the conversion factor between minutes and hours, when plugging
in. When dealing with time, 30 is usually a safer choice. So, write down x = 30.

Next, you need a number for y, which represents the number of hours. Again, you might be tempted to use
y = 24 but that’s the conversion factor between hours and days. So, y = 12 is a safer choice. Write down y
= 12.

Now, it’s time to solve the problem to come up with a target. If the watch loses 30 minutes every 12
hours, then it loses 60 minutes every 24 hours. Put another way, the watch loses an hour each day. In one
week, the watch will lose 7 hours. That’s your target so be sure to circle it.

Now, you just need to check the answer choices to see which one gives you 7 when x = 30 and y = 12.

A) 7 xy =   7(30)(12)   =   Something   too big!    Cross   it  off.

B)  =1. Also    wrong.

C)  Cross   it  off.