# FE Exam Calculator Tip – Solving for unknown variable “x”

To pass the FE exam (EIT Exam), it is crucial that you are very familiar with certain calculator functions that can drastically reduce the time you spend per question.

Passing the NCEES FE exam isn’t just about knowing the material, the test-taking and time saving strategies you employ are just as important. This quick post will discuss the handy “solver” method that allows you to solve for an unknown variable “x”.

The NCEES has a calculator policy allowing for the following calculator models during the 2021 FE exam:

• Casio: All fx-115 and fx-991 models (Any Casio calculator must have “fx-115” or “fx-991” in its model name.)
• Hewlett Packard: The HP 33s and HP 35s models, but no others
• Texas Instruments: All TI-30X and TI-36X models (Any Texas Instruments calculator must have “TI-30X” or “TI-36X” in its model name.)

For the FE exam we recommend that you use either the TI36X Pro or the Casio Fx-115 as these two have all the built in functions needed for the FE exam.

### Example 1: Using the solver to solve for unknown value “x”

The value of x in the expression $$142 e^{-2 x}=15$$ is most nearly:

(A) 1.15

(B) 1.25

(C) 1.12

(D) 1.14

Casio 115

TI-36X Pro

### Example 2: Using the solver to solve for unknown value “x”

For a given stress state, an element is subjected to a compressive stress of -60 MPa in the y-direction and a tensile stress of 45 MPa in the x-direction. The radius of the Mohr circle is 60.47 MPa. The shear stress (MPa) at this given stress state is most nearly:

(A) 25

(B) 30

(C) 7.5

(D) 10.5

Casio 115

TI-36X Pro