dans parents are going to pay for half his car if he gets a 90 average in math for all four marking periods and the final exam. Here are his grades for the first four quarters: 91,83,90 and 89. What grade does he need on his final exam to have a 90 average?

Above 97.

Step-by-step explanation:

The average of something is the total values divided by the number of values added together so:

Step 1 - Add the four values together:

Let x be the unknown final exam grade

91 + 83 + 90 + 89 + x

353 + x

Step 2 - Find the average value:

Step 3 - Simplify by multiplying both sides by 5:

Step 4 - Isolate x:

x = 450 - 353

x = 97

So his grade must be above 97.

Hope this helps!

step-by-step explanation:

to find if any function is an inverse of the other, put the first equation in as x in the next one. then simplify and solve. if at the end you get the statement y = x, then it is an inverse. if you get anything else, it is not.