Melody

921 Questions
34315 Answers

+1

1

1742

2

+118725

Mathigon website

I just discovered a site called mathigon

https://mathigon.org/dashboard
read more ..

Melody Apr 2, 2022

-8

609

1

+118725

Reporting problems.

There are a number of people having problems at the moment.
If you lodge an error can you please give all relevant information that you can think of.
Where you are in the world - the city or the country - is often very important information. read more ..

Melody Mar 16, 2022

-2

8

1459

5

+118725

How to make an empty rectangle in Latex

I just worked out how to make an empty box of various horizonal size easily in LaTex.
This is not a recommended method, but other methods that I have tried here have not worked.
This coding is really simple. Just put letters inside read more ..

●●●●●

Melody Mar 15, 2022

-3

871

3

+118725

HAPPY ANNIVERSARY CHRIS! (CPhill)

I just realized that you became a member here exactly 8 years ago today!

It has been great to have you here all that time

off-topic

Melody Mar 13, 2022

-4

849

3

+118725

WELCOME BACK CPHILL !

Melody Feb 11, 2022

-5

717

2

+118725

Very interesting question. No high level maths required.

This question was posted a couple of days ago.
https://web2.0calc.com/questions/geometry_73561

I think it is really interesting. It looks much more difficult than it really needs to be. read more ..

Melody Feb 1, 2022

-7

889

11

+118725

Members have a better experience. Their questions get more attention.

Almost everyone is posting as a guest.
If you post as a member your questions will have a far greater chance of a timely and helpful response.
If you are a genuine learner and interact with us, you will become known and answerers will do read more ..

●●●●●●●●●●●

Melody Jan 9, 2022

-6

1

996

3

+118725

HAPPY BIRTHDAY CHRIS!

Melody Dec 20, 2021

+5

16

5552

9

+118725

Some guidelines for question askers.

Please note:
1) Ask only one question per post.
2) When asking a question talk about what you have tried for yourself. Then people will take you more seriously and will be more able and willing to help.
3) If you get an answer read more ..

off-topic

●●●●●●●●●

Melody Nov 4, 2021

-9

1091

1

+118725

Remeniscing - a little historical humour.

I just found this old post that some of you, who have been around for a while, might find amusing.

https://web2.0calc.com/questions/look-at-the-new-leader-board

off-topic

Melody Oct 29, 2021

+118725

0

I am really glad that i could help you. I always like getting feedback and it is great when the feedback is so positive.
Thank you.

MelodyNov 26, 2013

+118725

0

if john and susie both collected 87 pieces of candy, and susie takes 13%, how many pieces does john have

Do you mean that they collected 87 peices each or 87 pieces altogether?

anyway
All the lollies put together is 100%
If Suzie gets 13% John gets the rest which will be 100-13% = 87%

So if there are 87 lollies altogether, John gets 87% of 87 = 87/100*87 = 75.69 lollies

MelodyNov 26, 2013

+118725

0

how would you figure out how many terminal zeroes are at the end of 1x2x3x4x5x6x7x8x9x10x11x12x13x14x15x16x17x18x19x20 WIThOUT using a calculator?
With a lot of time I think.

on a calc it is just 20! = 2.4390200817664 x 10^18

so that has 4 terminal zeros.

You taught me a new term - I had never heard of terminal zeros before.

MelodyNov 26, 2013

+118725

0

The annual profit, p(x), in dollars of a small company varies with the number of employees, x, as p(x) = -40x^2 + 4400x. What is the range of the number of employees for which the company’s annual profit will be at least $112,000?

p(x) = -40x^2 + 4400x

-40x^2 + 4400x >= 112000

-40x^2 + 4400x - 112000 >= 0

-40x^2 + 4400x - 112000 >= 0
divide everything by 40
-x^2 + 110x - 2800 >= 0

now times by -1 but don't forget that when you multiply an inequality by a neg, you have to turn the sign around
x^2 - 110x + 2800 <= 0
now you have to factorise to get the roots. I notice straight away that -4*-7=28 and -4+-7=-11 so I know what the factors are but if you don't see this you can use the quadratic equation.

(x-40)(x-70) <=0
When x=40, or x=70 this will equal 0

consider the graph
y=(x-40)(x-70)
the equation we want will be true if y is positive
this is the equation of a concave up parabola with roots at 40 and 70 (sketch it)
So y will be positive or zero 40<=x<=70

so to make a profit of at least $112000 the company need to have between 40 and 70 employees.

If anything doesn't make sense, please post again.

MelodyNov 26, 2013

+118725

0

square root w-8=8

(square root w)-8=8

(square root w)-8+8 =8+8

I think you can finish it . If no then post again.

MelodyNov 26, 2013

+118725

0

D=5*e^(-0.4h)

Find h when D=2

2=5*e^(-0.4h)
divide both sides by 5
0.4 = e^(-0.4h)

ln 0.4 = lne^(-0.4h)

ln 0.4 = -0.4h

h = ln0.4 / -0.4 = 2.29072683hours

h = 2 hours and 17 minutes to the nearest minute.
-----------------------------
now looking at your specific concerns
1) what to do with the 5 when turning it into log form (hopefully you can see what happened to the 5)

2) and also how is the answer positive with the -.4h.

-0.4h is the power of e. Any positive number raised to any number (positive or negative) will be positive. e is a positive number.

I don't know how good you can manipulate indices but maybe if you think about this it might help

16^(-0.5) = 1 / 16^(0.5) = 1 / the sqrt of 16 = 1/4

MelodyNov 26, 2013

+118725

0

I just want to clarify
is it

D=5*e^(-0.4h)
or
D=5*e^(-0.4)*h = 5*h*e(-0.4) [tecnically this is what you have written]

MelodyNov 26, 2013

+118725

0

what is two to the negative fifth power?

It is 1/ two to the positive fifth power

when you want to get rid of a negative power you swap the whole thing to the other side of the fraction line and change the negative to a positive.

When you say 5th do you mean a power of 1/5 OR do you mean a power of 5?

MelodyNov 26, 2013

+118725

0

what is the multiplicative inverse or reciprocal inverse of 4/9

The reciprocal is 9/4
The inverse is 9/4

The reciprocal inverse makes no sense to me.

MelodyNov 26, 2013

+118725

0

Can't you at least start it in your own calculator?

MelodyNov 26, 2013