# After substituting, what is the first step when evaluating x+3x-4.2 when x=5?

Jan 13, 2017

Look at PEMDAS for guidance.

#### Explanation:

After substituting $x = 5$ into the mathematical expression $x + 3 x - 4.2$, it will become $5 + 3 \left(5\right) - 4.2$

PEMDAS states the order of operations as followed:
P arentheses
E xponents/Square Roots
M ultiplication/D ivision
A ddition/S ubtraction

What this means is that you are supposed to do whatever is in the parentheses first. Then you are supposed to do exponents and square roots. After that, multiplication and division (from left to right), and finally, addition and subtraction (also from left to right).

In this problem, we look at the parentheses and it's just a $5$ in it. There's noting we can do wit that, so we move on to exponents/square roots. There is no exponents nor square roots so we move on to multiplication/division. Here, we can multiply $3$ by $5$ to get $15$.

So the first step after evaluating $x + 3 x - 4.2$ when $x = 5$ is to multiply $3$ by $5$.