10 students averaged 80, so the sum of their scores was (10 x 80) = 800
20 students averaged 89, so the sum of their scores was (20 x 89) = 1,780
All together, the sum of all 30 scores was (800 + 1,780) = 2,580
30 students totaled 2,580, so their average was (2,580 / 30) = <em> 86</em> .
Answer:
D. 2/7
Step-by-step explanation:
The probability is calculate as a division between the number of ways in which Andrew will be selected and karen will not and the total ways in which they can select 4 people from a group of 8 volunteers.
The number of ways in which they can select 4 people from a group of 8 volunteers can be calculated using:

Where nCk give as the number of ways in which we can form groups of k elements from a group of n elements.
So, if we replace n by 8 and k by 4, we get:

Then, there are 70 ways to select 4 people from a group of 8 volunteers.
At the same way, the number of ways in which Andrew will be selected and karen will not can be calculate replacing n by 6 and k by 3 in the same equation as:

We replace n by 6 because from the 8 volunteers, Andrew is going to be selected and Karen will not, so, the people that affect the result are just the 6 remaining volunteers. Also, k is equal to 3 because Andrew is already selected and we just need to select 3 more people.
Finally, the probability is:

Answer:
(1/2,4)
Step-by-step explanation:
First, determine y in first equation: 2x+y=5 or y=5-2x
replace value of y determined in first equation (5-2x) into 2nd equation
4x-3(5-2x)=-10
4x-15+6x=10
10x=5
x=1/2
put value of x into either equation to solve for y so
2(1/2)+y=5
1+y=5
y=4
answer: x=1/2, y=4
check answer by substituting x and y into either equation:
4x-3y=-10
4(1/2)-3(4)=-10
2-12=-10
-10=-10
or
2x+y=5
2(1/2)+4=5
1+4=5
5=5
I might be wrong but, I would say about 32.6 miles a day. This could be wrong.