Question 53351
Let the lowest grade be x.
Let the highest grade by y.
<br>x + y = 135 (equation 1) [This means that the sum of the highest and lowest grade is 135]
y = 3x - 9 (equation 2) [This means that the highest grade is 9 points lesser than 3 times the lowest grade]
<br>We will now substitute equation 2 into equation 1.
x + (3x - 9) = 135  [The y in equation 1 is now (3x - 9) from equation 2]
4x - 9 = 135
4x = 144
x = 36
We now know that the lowest grade is 36.
<br>y = 135 - 36
y = 99
The highest grade is 99.