An instructor gives a 100 point exam and decides that a score of 90 or above will be a grade of 4.0, a score of 40 or below will be a grade of zero, and between 40 and 90 the grading will be linear. Let x be the exam score and let y be the corresponding grade. Find a formula which applies the scores x, between 40 & 90.

Question

anonymous · Answer

I have figured the slope to be 2/25 but cannot determine the b value in the equation 
y = mx+ b

swissgirl · Answer

We know 2 points on the graph
At x=40 then y=0 
and at x=90 then y=4
Plug in one of the following point into your equation and solve for b

anonymous · Answer

Man... So easy. Thank you!

anonymous · Answer

Y=2/25x- 16/5