How to do answer 16, 19 and 21? Please show me the solutions.

Mathematics

2 answers:

Pepsi [2]3 years ago

8 0

Answer:

The speed in still air = 200 mph.

Step-by-step explanation:

21.

If the speed of the plane in still air is x mph then with the wind its speed is x+20 mph and against the wind it is x - 20 mph. Also let t hours be the time taken for the journey with the wind.

So we have the 2 equations:

x + 20 = 396 / t

x - 20 = 396 / (4 - t)

Subtracting to eliminate x

40 = 396 / t - 396 / (4 - t)

40t(4 - t) = 396(4 - t) - 396t

160t - 40t^2 = 1584 - 396t - 396t

-40t^2 + 952t - 1584 = 0

Dividing through by 8:

-5t^2 + 119t - 198 = 0

Using the quadratic formula we get t = 22, 1.8 hours . We ignore the 22 because the total time is 4 hours.

So the speed x = is found by plugging in t 1.8:

x + 20 = 396/1.8

x = 200 mph.

Zolol [24]3 years ago

6 0

Answer:

16) the boy is 11 years old

Step-by-step explanation:

16) Let the boy’s present age be b.

b+5 = 4(b-9)^2, or

b+5 = 4[b^2–18b+81] = 4b^2–72b+324, or

4b^2–73b+319 = 0, or

(4b-29)(x-11) = 0, or

b = 11 or 7.25 years. The second value is inadmissible.

So the boy is 11 years old, now.

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Identify as a direct variation, inverse variation or neither. The number of tons of coal burned by an old coal burning locomotiv

pochemuha

Answer: it is a direct variation.

Justification:

In a direct variation the variables are related by a proportionality constant in this way:

y = k x

Tthan means that the value of y is always the product of a constant times the value of x.

The situation discribed for the coal may be written as:
number of tons of coal burned: c

number of hours: h

⇒ c = k × h

Which is that you can calcualte the number of tons of coal burned at any time, once you know the proportionality constant k.

5 0

4 years ago

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Nikolay [14]

The value 0.92 indicates the relative density of the ice.

Data;

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<h3>Specific Gravity</h3>

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mathematically;

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