<span>Jerry is 8 years younger than Patricia, so:
(1): Jerry = Patricia - 8
Six years ago, Patricia was 3 times as old as Jerry was then, so:
(2): (Patricia - 6) = (Jerry - 6)*3
Putting equation 1 in to equation 2
(Patricia - 6) = (Patricia - 8 - 6)*3
Patricia - 6 = 3Patricia - 42
36 = 2Patricia
Patricia = 18
And so Jerry = 10</span>
An equation for the parabola would be y²=-19x.
Since we have x=4.75 for the directrix, this tells us that the parabola's axis of symmetry runs parallel to the x-axis. This means we will use the standard form
(y-k)²=4p(x-h), where (h, k) is the vertex, (h+p, k) is the focus and x=h-p is the directrix.
Beginning with the directrix:
x=h-p=4.75
h-p=4.75
Since the vertex is at (0, 0), this means h=0 and k=0:
0-p=4.75
-p=4.75
p=-4.75
Substituting this into the standard form as well as our values for h and k we have:
(y-0)²=4(-4.75)(x-0)
y²=-19x
He must get a 65 as a minimum grade on his third test to get an average of 70.
Equation is
85 + 60 + x
------------------- greater than or equal to 70
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