A machine costs m dollars per day to maintain

canbtg wrote:A colony of ants increases its population by 4 percent. If after this increase, bacteria deplete the population by , the new ant population is what percent of the original ant population?


A)16%


B)26%


C)29%


D)50%


E)78%

You're missing part of the question here.
We need to know the percent reduction caused by the bacteria.

Cheers,
Brent

canbtg wrote:A machine costs m dollars per day to maintain and n cents for each unit it produces. If the machine is operated 7 days a week and produces r units in a week, which of the following is the total cost, in dollars, of operating the machine for a week?

A) 7m + 100nr
B) 7m + nr/ 100
C) 7m + nr
D) 7m + 100nr/100
E) 700mnr

TOTAL cost = maintenance cost + production cost

This machine costs m dollars per day to maintain, and the machine is operated 7 days.
So, the total maintenance cost = 7m dollars

The machine costs n CENTS for each unit it produces.
Since the question asks for the total cost in DOLLARS, we can convert n CENTS to n/100 DOLLARS
If the machine produces r units, then the total production cost = (n/100)(r) = rn/100 dollars

So, TOTAL cost = 7m + rn/100 dollars

Answer: B

Cheers,
Brent

Hi canbtg,

This question can also be solved by TESTing VALUES.

We're told that there are 2 costs with running a machine:

M DOLLARS per day to maintain it
N CENTS per unit that it produces

We're told that R units are produced over the course of 7 days. We're asked for the cost, IN DOLLARS of operating the machine during that time.

Let's TEST VALUES:

M = 2
N = 3
R = 200

Over the course of 7 days, we spent ($2/day)(7 days) to maintain the machine and (3 cents)(200 units) on the units. Thus, we spent $14 + $6.00 = $20

The only answer that matches is B

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