Answer:
(27.3692 ; 44.6308)
Step-by-step explanation:
Mean, xbar = 36
Standard deviation, s = 11
Sample size, n = 12
Tcritical at 0.2, df = 12 - 1 = 11 ; Tcritical = 2.718
Confidence interval :
Xbar ± Margin of error
Margin of Error = Tcritical * s/sqrt(n)
Margin of Error = 2.718 * 11/sqrt(12) = 8.6308
Confidence interval :
Lower boundary : 36 - 8.6308 = 27.3692
Upper boundary : 36 + 8.6308 = 44.6308
(27.3692 ; 44.6308)
This problem can be solved by the chicken rabbits method or you can just do simple algebra.
I.) Chicken and rabbits method
First assume all 110 coins are dimes and none are quarters.
We will have a total value of 11 dollars
Now for each dime we switch out for a quarter, we adds 15 cents to the total value.
18.50-11=7.50 dollars
There are 750/15=50 group of 15 cents in the 7 dollars and 50 cents.
This also meant that we need to switch out 50 dimes for 50 quarters.
So we have 50 quarters.
That first method is very good and very quick once you get the hang of it, now I'm going to show you the algebraic way to solve this.
Let's say there are x dimes and y quarters.
Set up equation
x+y=110
10x+25y=1850
Now solve multiply first equation by 10
10x+10y=1100
subtract
15y=750
y=50
Now we set the numbers of quarters to y so the answer is 50 quarters.
I personally recommend using algebra whenever you can because the practice is very important and you will eventually get really fast at setting up and solving equations. The first method is faster in this case but the second is more generalize, hope it helps.
