4.
Xavier and Yifei have been married for exactly 10 years.
Yifei is seven years older than Xavier.
Now the
sum of their ages is 67.
How old was Yifei when they were married?
(6 points)
a. Write an equation that represents the unknown ages in terms of
Yifei's
age when they were married.
(Y =Yifei's age when married, X = Xavier's age when married)
Y = x+7
X = y-7
(y+10)+(y-7+10) = 67
Y+10 + Y+3
2y+13=67
2y=54
Y=27
b. Determine how old Yifei was when Yifei and Xavier were married. (Solve your equation(s) for Y)
27 Years old.
5. The cost of cleaning up pollution in a stream is given by
࠵? =
%&'''
('')*
, where
C
is the cost in dollars to
clean
p
percent of the stream.
(For instance, when
p
is 20, then the formula will calculate the cost to clean up 20
percent of the stream.)
p
must be greater than or equal to zero and
p
must be less than what number?
Why?
(5 points)
P must be greater than zero because there is always going to be pollution to clean up, and an unreleastic
number would be zero because there is no chance.