Answer:
Options: A, B, and C correctly solve for x.
Step-by-step explanation:
A).
=
Multiplying both sides by 2 gives;
5x = 15
x = 15 ÷ 5 = 3
∴ This option correctly solve for x.
B).
x + = 7
x = 7 - =
∴ This option correctly solve for x.
C).
x + 3 =
x =
But the option give x as 5/6 hence this option does not correctly solve for x.
D).
5x = 11/2
x = 11/2 ÷ 5 = 11/2 × 1/5 = 11/10
But the option gives x as 10/11 so it does not correctly solve for x.
Answer:
Speed of Current = 5 miles per hour
Step-by-step explanation:
We know distance formula,
D = RT
Where
D is distance
R is rate
T is time
If we let speed of boat (assume) to be "x" and speed of current to be "c"
Then downstream rate is (with current) = x + c
Upstream rate is (against current) = x - c
40 mins to go 20 miles downstream, that means:
D = RT
20 = (x + c)(40)
and
60 minutes to go upstream, 20 miles, that means:
D = RT
20 = (x - c)(60)
Simplifying first equation:
40x + 40c = 20
Simplifying second equation:
60x - 60c = 20
Multiplying first equation by 60, we get:
60 * [40x + 40c = 20] = 2400x + 2400c = 1200
Multiplying second equation by 40, we get:
40 * [60x - 60c = 20] = 2400x - 2400c = 800
Now we add up both these equations:
2400x + 2400c = 1200
2400x - 2400c = 800
----------------------------------
4800x = 2000
x = 2000/4800 = 5/12
We need speed of current, that is "c", so we plug in the value of x into first equation and solve for c:
Speed of Current = 1/12 miles per minute
Since there is 60 minutes in an hours, that would be:
(1/12) * 60 = 5 miles per hour
Speed of Current = 5 miles per hour