David rowed a boat upstream for three miles and then returned to point he started from. The entire journey took four hours.
The speed of the stream is one mile per hour.
Find David's speed in still water.
David's speed in still water is ? miles per hour?

Answers

Answer 1

Answer: The speed of the stream: v s = 1 mph
v - David`s speed in still water
( v - 1 ) t 1 = 3
( v + 1 ) t 2 = 3
t 1 + t 2 = 4
---------------------------
t 2 = 4 - t 1
3 = ( v - 1 ) * t 1
3 = ( v + 1 ) * ( 4 - t 1 )
-----------------------------
3 = v t 1 - t 1
+
3 = 4 v - v t 1 + 4 - t 1
------------------------------
6 = 4 v + 4 - 2 t 1
2 = 4 v - 2 t 1
2 t 1 = 4 v - 2 / : 2 ( divide both sides of equation by 2)
t 1 = 2 v - 1
t 2 = 5 - 2 v
------------------
3 = ( v - 1 ) * ( 2 v - 1 )
3 = 2 v² - 3 v + 1
2 v² - 3 v - 2 = 0
v 1/2 = 3+/- √(9 + 16 ) / 4 = (3 + 5)/4 = 8/4 = 2 ( other solution is negative )
Answer: David`s speed in still water is 2 miles per hour.

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How to solve linear equations by substitution?

5x+2y=9
x+y=-3

Answers

5x+2y=9 x+y=3

change x+y=3 into x=3-y

plug that equation into 5x+2y=9 where x is.

5(3-y)+2y=9

then distribute.

15-5y+2y=9

15-7y=9

minus 15.

-7y=-6

divide both sides by -7.

y is equal to -6/7.

then go back to the first equation and plug in for y.

and then you will get x.

then you will have (y,x)

$\begin{cases} 5x+2y=9 \n x+y=-3\end{cases} \n \n\begin{cases} 5x+2*(-3-x)=9 \n y=-3 -x\end{cases} \n \n\begin{cases} 5x-6-2x =9 \n y=-3 -x\end{cases}\n \n\begin{cases} 3x =9+6 \n y=-3 -x\end{cases}$

$\begin{cases} 3x =15 \ \ /:3 \n y=-3 -x\end{cases} \n \n\begin{cases} x =5 \n y=-3 -5\end{cases} \n \n\begin{cases} x =5 \n y=-8\end{cases}$

Solve this..➕+ ➕ + ➕+ ➕=30
Fill the boxes using (1, 3, 5, 7, 9, 11, 13, 15)
U can also repeat the numbers..

Answers

These are all possible combinations:
1 , 1 , 13 , 15
1 , 3 , 11 , 15
1 , 3 , 13 , 13
1 , 5 , 9 , 15
1 , 5 , 11 , 13
1 , 7 , 7 , 15
1 , 7 , 9 , 13
1 , 7 , 11 , 11
1 , 9 , 9 , 11
3 , 3 , 9 , 15
3 , 3 , 11 , 13
3 , 5 , 7 , 15
3 , 5 , 9 , 13
3 , 5 , 11 , 11
3 , 7 , 7 , 13
3 , 7 , 9 , 11
3 , 9 , 9 , 9
5 , 5 , 5 , 15
5 , 5 , 7 , 13
5 , 5 , 9 , 11
5 , 7 , 7 , 11
5 , 7 , 9 , 9
7 , 7 , 7 , 9

There can be a lot many solutions for the above question
some of them are
9+11+5+5=30
it can also be solved as
15+5+5+5=30
also
13+7+5+5=30

Can someone help me with this math homework please!

Answers

Answfirst one

Step-by-step explanation:

hope it helps thank u

Answer:

first one

Step-by-step explanation:

2 students have the same age but different heights.

since age is the input and height is the output. in order to be a function one must have exact one output for one input.

since the heights of students in Tessa 's class are not a function of their ages (one input must have two outputs) two students of same age must have different heights.

Graph y=−4/7x+1 . Please help.

Answers

Answer:

The required graph is shown below.

Step-by-step explanation:

Consider the provided function.

$y=-(4)/(7)x+1$

The above function is a linear function.

We can draw the graph of the function with the help of 2 points.

Substitute x = 0 in the above function.

$y=-(4)/(7)(0)+1$

$y=1$

Substitute y = 0 in the above function.

$0=-(4)/(7)x+1$

$(4)/(7)x=1$

$x=(7)/(4)$

Now plot the points.

Draw a straight line passing through (0,1) and (7/4,0)

The required graph is shown below.

Go to a website called desmos graphing calculator and it will help you out but I put a image of the graphed equation as well.

The element in group 15 and period 4

Answers

Final answer:

The element in group 15 and period 4 of the periodic table is Arsenic (As), which is classified as a metalloid due to its mixed properties of metals and non-metals.

Explanation:

The element that is found in group 15 and period 4 on the periodic table is Arsenic (As). Group refers to the vertical column and period refers to the horizontal row on the periodic table.

Arsenic belongs to the 'p-block' group of the periodic table and it is classified as a metalloid. This means it has properties of both metals and non-metals. For example, arsenic is brittle (like a non-metal) but can also conduct some electricity (like a metal).