Answer:
Step-by-step explanation:
Answer:

Step-by-step explanation:
Let
x------> the number of days
y----> the cost of renting a car
we know that
For 

For 
The rate is equal to

so

In this problem. the car has been rented for more than a week
therefore

The cost of renting a car is equal to

Answer:
$1.25
September
$30
Step-by-step explanation:
Let's take this a step a time.
First we need to find how much the price of the flowers were in September.
We know that each flower cost $1.50 on October.
The October price was a 20% increase of the September price.
To calculate for the price of the flowers on September, we can solve it like this:
Let x = Price during September
1.2x = 1.50
We used 1.2 because the price of $1.50 is 120% of the original price.
Now we divide both sides by 1.2 to find x.

x = 1.25
The price of the flowers during September was $1.25 each.
Now the 7th grade class earned 40% of the selling price of each flower.
40% = 0.40
To find how much they made on each month, we simply multiply the percentage to the price and the number of flowers sold.
September = 0.40 x 1.25 x 900
September = 0.5 x 900
September = $450
Now for October.
October = 0.40 x 1.50 x 700
October = 0.6 x 700
October = $420
The 7th Graders earned more on September.
They earned $30 more on September than October.
We want to see how long will take a healthy adult to reduce the caffeine in his body to a 60%. We will find that the answer is 3.55 hours.
We know that the half-life of caffeine is 4.8 hours, this means that for a given initial quantity of coffee A, after 4.8 hours that quantity reduces to A/2.
So we can define the proportion of coffee that Jeremiah has in his body as:
P(t) = 1*e^{k*t}
Such that:
P(4.8 h) = 0.5 = 1*e^{k*4.8}
Then, if we apply the natural logarithm we get:
Ln(0.5) = Ln(e^{k*4.8})
Ln(0.5) = k*4.8
Ln(0.5)/4.8 = k = -0.144
Then the equation is:
P(t) = 1*e^{-0.144*t}
Now we want to find the time such that the caffeine in his body is the 60% of what he drank that morning, then we must solve:
P(t) = 0.6 = 1*e^{-0.144*t}
Again, we use the natural logarithm:
Ln(0.6) = Ln(e^{-0.144*t})
Ln(0.6) = -0.144*t
Ln(0.6)/-0.144 = t = 3.55
So after 3.55 hours only the 60% of the coffee that he drank that morning will still be in his body.
If you want to learn more, you can read:
brainly.com/question/19599469