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erma4kov [3.2K]
4 years ago
6

One person can do a certain job in twenty-one minutes, and another person can do the same job in twenty-eight minutes. How many

minutes will it take them to do the job together?
6 min
12 min
24 min
Mathematics
2 answers:
grigory [225]4 years ago
6 0

the correct answer is 12

MrMuchimi4 years ago
6 0

Answer: 12 min

Step-by-step explanation:

Given: Time taken by one person to do a job = 21 minutes

Time taken by another person to do a the same job = 28 minutes

If they work together then the total time taken by both of them to complete the job is given by :-

\frac{1}{T}=\frac{1}{21}+\frac{1}{28}\\\\\Rightarrow\frac{1}{T}=\frac{4+3}{84}\\\\\Rightarrow\frac{1}{T}=\frac{7}{84}\\\\\Rightarrow\frac{1}{T}=\frac{1}{12}\\\\\Rightarrow T=12

Hence, they will take 12 minutes to do the job together.

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<span>Find the wind speed and the plane's airspeed.
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Let s = speed of the plane in still air
Let w = speed of the wind
then
(s-w) = plane speed against the wind
and
(s+w) = plane speed with the wind
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Change 3 3/8 hrs to 3.375 hrs
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The trips there and back are equal distance, (1890 mi) write two distance equations
dist = time * speed
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3.375(s-w) = 1890
3.0(s + w) = 1890

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It is convenient that we can simplify both these equations:
divide the 1st by 3.375
divide the 2nd by 3
resulting in two simple equations that can be used for elimination of w
s - w = 560
s + w = 630
----------------adding eliminates w, find s
2s = 1190
s = 
s = 595 mph is the plane speed in still air
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595 + w = 630
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3 0
4 years ago
Find the solution of the system of equations.
Alex17521 [72]

Answer:

the answer is Solve for the first variable in one of the equations, then substitute the result into the other equation.

Point Form:

(−17/2, -7)

Equation Form:x=-17/2 y=-7

5 0
3 years ago
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It takes Mark 3 minutes to make 1 1/2 inches of a bracelet. If he works at the same speed, how many minutes will it take him to
RUDIKE [14]

Answer:

  24 minutes

Step-by-step explanation:

Working at the same speed, the ratio of time to length is the same:

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It will take Mark 24 minutes to make a 12-inch bracelet.

7 0
4 years ago
At 1:00 pm the water level in a pool is 13 inches. At 1:30pm the water level is 18 inches. At 2:30pm the water level is 28 inche
SashulF [63]
From the given question we come to know of certain number of facts and they are:
At 1:00 PM the water level of the pond was = 13 inches
At 1:30 PM the water level of the pond was = 18 inches
At 2:30 PM the water level of the pond was = 28 inches
From the above given facts we can easily find the amount of water changing every half an hour.
Amount of increase in water from 1:00PM to 1:30 PM = (18 - 13) inches
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Amount of increase in water level from 1:30PM to 2:30PM = (28 -18) inches
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From the above two deductions we can come to the conclusion the the constant rate of change in water level is 5 inches for every half an hour.
4 0
3 years ago
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Answer:

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4 0
3 years ago
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