David received a 20% tip on a bill of $86.40. how much was his tip?

To find the tip of the bill. You will need to find how much of $86.40 is 20%. In this question, they're asking how much is the tip, not how much will the final price be.

When you multiply a percentage you move the decimal point 2 times to the left: 20. → .20

You would multiply $86.40 by .20

When you solve it 86.40 × .20 = 17.28

$17.28 is 20% of $86.40

$17.28 will be the amount he got for his tip.

My mom keeps saying i need to know how to do this in my head. I'll do it with a calculator just to be safe lol.

So to do this all we have to do is multiply 86.40 x .20 and we get  $17.28

$17.28<--- Answer.

-Seth

for this pair of functions g(x)=x-2 and f(x)=|x| is (g o f)(a)= |a| -2

step-by-step explanation:

g(x)=x-2

f(x)=|x|

(g o f)(a)=?

(g o f)(x)=g(f(x))

(g o f)(x)=g(|x|)

(g o f)(x)=|x|-2

(g o f)(a)=|a|-2

it has to have an angle of 90 degrees