Answer:
- The system of equations is x + y = 85 and 7/20x+2/5y=31
- To eliminate the x-variable from the equations, you can multiply the equation with the fractions by 20 and multiply the other equation by -7.
- B-She used 60 minutes for calling and 25 minutes for data.
Step-by-step explanation:
It is always a good idea to start by defining variables in such a problem. Here, we can let x represent the number of calling minutes, and y represent the number of data minutes. The the total number of minutes used is ...
x + y = 85
The total of charges is the sum of the products of charge per minute and minutes used:
7/20x + 2/5y = 31.00
We can eliminate the x-variable in these equations by multiplying the first by -7 and the second by 20, then adding the result.
-7(x +y) +20(7/20x +2/5y) = -7(85) +20(31)
-7x -7y +7x +8y = -595 +620 . . . . eliminate parentheses
y = 25 . . . . . . . . simplify
Then the value of x is
x = 85 -y = 85 -25
x = 60
Explanation:
There may be a couple of reasons for this:
1. Each team represents a sample of the players in the league. The averages of (random) samples can be expected to have a standard deviation that is smaller than the population standard deviation by a factor related to sample size.
2. A team average will result from the players who are played the most. Each team can be expected to field players more often whose averages are among the highest. The standard deviation of a set of the top tier of players will necessarily be smaller than the standard deviation of the set of all players.
Smallest 1/4 5/12 1/2 2/3 3/4 biggest
