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SAT Math: Algebra

Functions

Let the function be defined by f(x) = 5x - 10.  If 2f(m) = 20, then what is the value of f(3m)? 

Knowsys Method

Read the problem carefully.  This is a grid in question.  Instead of bubbling in a letter, you will bubble in your answer.  You should always guess on grid in questions because, unlike multiple choice questions, grid in questions do not have a wrong answer penalty. 

Identify the bottom line.  f(3m) = ?

Assess your options.  This function problem is very straightforward.  All you have to do is plug in the information given to you and solve. 

Attack the problem. 

2f(m) = 20, so f(m) = 10

If f(x) = 5x - 10, then f(m) = 5m - 10.  Set that equal to the value you already know for f(m) and solve for m.

10 = 5m - 10
20 = 5m
4 = m

Now plug in the value of m to find f(3m).

f(3m) = f(12) = 5(12) - 10 = 50

Loop back.  Verify that you solved for the bottom line.

The correct answer is 50.

This is a medium level problem.  

Want some help reviewing the math concepts you need to master?  Try out the Knowsys Pre-Algebra Flashcards, the Knowsys Algebra I Flashcards, and the Knowsys SAT & ACT Math Practice book.  

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