## Functions

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

## 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*(3*m*) = ?

**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.**

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

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

10 = 5*m* - 10

20 = 5*m*

4 = *m*

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

*f*(3*m*) = *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.

Subscribe to Knowsys SAT & ACT Blog by Email