Answer:
Option A.
Step-by-step explanation:
We know that we have:
220 students in grade 6.
170 students in grade 7.
100 students in grade 8.
Now we want to make a sample, to have the sample in the most representative way, so we should select the same percentage of students for each grade.
Let's analyze option A (this is the one that makes sense because has the larger number for 6th grade, then 7th grade and last for 8th grade)
Here we need to look at the quotient between the number of students selected for each grade, and the total number of students in the grade:
for 6th grade:
45/220 = 0.2
for 7th grade:
35/170 = 0.21
for 8th grade:
20/100 = 0.2
In the 3 cases we can see that we have almost the same ratio, which means that for the sample we selected around the 20% of each grade.
This is the most representative way of sampling in this case, then the correct option is A.
<h3>
Answer: 14 km per hour</h3>
=====================================================
Work Shown:
x = rowing speed when there is no current
c = speed of the current
speeds are in km per hour
-----------
Going downstream, i.e. with the current:
x+c = faster speed since the current is pushing you
distance = rate*time
d = r*t
40 = (x+c)*2
x+c = 40/2
x+c = 20
c = 20-x
-----------
Going upstream, i.e. against the current:
x-c = slower speed since the current is working against you
d = r*t
16 = (x-c)*2
16 = 2x-2c
2x-2c = 16
2(x-c) = 16
x-c = 16/2
x-c = 8
x-(20-x) = 8 ... plug in c = 20-x
x-20+x = 8
2x-20 = 8
2x = 8+20
2x = 28
x = 28/2
x = 14 km per hour is the rowing speed when there is no current
Side note: the speed of the current is c = 20-x = 20-14 = 6 km per hour.
| 3x - 1 | + 7 = 2
| 3x - 1 | = 2 - 7
| 3x - 1 | = -5.....no solution because an absolute value cannot equal a negative number.
| 2x + 1 | + 4 = 3
| 2x + 1 | = 3 - 4
|2x + 1 | = -1...same thing...no solution..cannot equal a neg. number
so Eq. 1 and Eq. 2 both have NO SOLUTIONS :)
It is 7 , 21
That’s the answer
Explenatkon.
