Cracking The SAT Premium

Don’t   Forget  to  Share

the Love

Don’t   forget  that    when    you

subtract    an  entire  equation,

you need    to  subtract    each

component   of  the equa-

tion—in simpler terms,

change  each    sign    to  the

opposite    operation,  and

then    add the equations.

Neither of these answers appears to be what the test writers are asking for, but on closer inspection, the
equation that resulted from subtraction can be multiplied by 2 to get the expression in the question.

2(–5a   –   1b  +   1c) =   2(–26)

–10a    –   2b  +   2c  =   –52

Solving for Variables in Simultaneous Equations

Shortcuts are awesome, so take them whenever you can on the SAT. But occasionally, you won’t have the
option of using a short-cut with simultaneous equations, so knowing how to solve for a variable is
imperative.

Here’s an example:

If  3x  +   2y  =   17  and 5x  −   4y  =   21, what    is  the value   of  y   ?

Here’s How to Crack It

In this case, the stack and solve method doesn’t bring us an immediate answer:

Neither of these methods gives you the value of y. The best way to approach this question is to try to
eliminate one variable. To do this, multiply one or both of the equations by a number that will cause the
other variable to have a coefficient of 0 when the equations are added or subtracted.