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## #1 Re: Help Me ! » Geometry and probability » Today 14:17:01

bobbym wrote:

Yes, without replacement there are 5 x 4 total choices. With replacement there are 5 x 5 total choices.

Bobbym, could you explain 1 ? Did you use Chinese Remainder theorem on no 1?

## #2 Re: Help Me ! » Geometry and probability » Today 13:55:51

bobbym wrote:

Hi;

But 3/20 would be without replacement, right?

## #3 Re: This is Cool » Interesting Graphs- » Today 13:06:08

bobbym wrote:

Hi;

If we could get that on the end of a line we could use it as bait. Might catch a nice Mackerel.

haha bobbym you are quite good at humor.

## #4 Re: Help Me ! » Geometry and probability » Today 13:04:44

bobbym wrote:

Hi;

1. n mod 122 = z
n mod 141 = z
n mod 179 = z.
Find two values of z and n that satisfy the equation above.
2. If x + y = xy, and x and y > 1, y=
a) x/(x-1), b)(x+1)/x, c)(x-1)/x, d)x/(x+1).
Manipulating the equation, I could not get one of the anwsers shown above.
3. 10,10,15,18,27 are numbers of a set N.
Find the probability when 2 randomly chosen numbers are in the ratio of 2:3. The 2 tens in the list are DISTINCT, i.e, 1st 10 and 15 and 2nd 10 and 15 are different.
I got 3/20 for this.
4.

4 seems to have been lost in the Bermuda Triangle.

For number 3, with.

## #5 Help Me ! » Geometry and probability » Today 11:21:52

Mathegocart
Replies: 7

1. n mod 122 = z
n mod 141 = z
n mod 179 = z.
Find two values of z and n that satisfy the equation above.
2. If x + y = xy, and x and y > 1, y=
a) x/(x-1), b)(x+1)/x, c)(x-1)/x, d)x/(x+1).
Manipulating the equation, I could not get one of the anwsers shown above.
3. 10,10,15,18,27 are numbers of a set N.
Find the probability when 2 randomly chosen numbers are in the ratio of 2:3. The 2 tens in the list are DISTINCT, i.e, 1st 10 and 15 and 2nd 10 and 15 are different.
I got 3/20 for this.
4. Adam could not remember his 3 digit combo to his combo lock at school. He remembered that the 3 digits were 1,3, and 4, but not the order. Nor did he remember if he turned it counter clockwise or clockwise after the first number. He did remember that he, after the 2nd number, turned it in the opposite direction than he did after the first number. How many different ways does Adam have to try to be sure he opens his lock?12?
5. There are 3 people Anne Beth and Carles. They all put their hats on top of their books. Anne, Beth and Carles grab a hat without looking(i.e, randomly.). What is the probability that noone chooses their own hat? . WITHOUT REPLACEMENT. Is this 5/6?
6.An classroom with 10 rows of seats has 10 seats in the front row, 11 seats in the 2nd row...students are permitted to sit in any row, but any student cannot sit next to another student. What is the MAXIMUM number of students that can be seated in the class.

## #6 This is Cool » Interesting Graphs- » 2016-07-28 23:33:18

Mathegocart
Replies: 3

I have created a exquisite graph called "Whiplash".
https://www.desmos.com/calculator/tc5yacacie
The graph lashes out, having some nice tangents and cosines stuck in it. The x^2 part amplifies it.

## #7 Re: Help Me ! » differentiation » 2016-07-28 23:20:20

Zeeshan 01 wrote:

why y is not constant if dxy\dx

We hold both of them constant.

## #8 Exercises » Quickies #5, Mathematics. » 2016-07-28 23:17:24

Mathegocart
Replies: 4

1)One dimension of Bobbym's cube is increased by 1, another is decreased by 1, and the third is left unchanged. The volume of the new rectangular solid is 5 less than that of the cube. What was the volume of the cube?

2) http://prntscr.com/bz0rqb Find x.

3. What are the last 5 digits of $9^{12}+3^{15}$
4. What is the remainder when 979^109 is divided by 3?
5. Find all values that satisfies $sin^{-2}+cos^{-2}=1.$. If there are none, write None.
6. It is often that students confuse
$cos^{2}$ and $cos(x^{2})$, when do these 2 expressions equal each other?
7. if http://prntscr.com/bz0o1o, Find P/Q.
8.What is i!, where i is the square root of -1.
9. Find the unit digit of $2^{10092}$ x 3^10221
10. Find the unit digit of 11^182.

## #9 Re: Help Me ! » Olympiad mathematical problems » 2016-07-28 22:47:24

Yes! I have gotten 4.

## #10 Re: Help Me ! » Olympiad mathematical problems » 2016-07-28 22:46:01

penbowl wrote:

Problem no. 2.      Ans: 20%
T salary=x
S salary=1.5 x
Let increment= y%
1.5 x-1.5 x(y/100)= x+x(y/100)
150x-1.5xy=100x+xy
50x=2.5xy
y=50x/2.5x=20%

I have the same anwser! cheers

## #11 Re: Help Me ! » e and ln » 2016-07-28 22:17:24

bobbym wrote:

e is maybe the most important constant in mathematics. It is a number and its value is approximately

actually not enough digits

## #12 Re: Help Me ! » let A ???? » 2016-07-28 22:15:48

Zeeshan 01 wrote:

If you use Chrome, I'd suggest getting Lightshot, a extension for Chrome that automatically upload

## #13 Re: Help Me ! » Olympiad mathematical problems » 2016-07-28 12:44:29

bobbym wrote:

Hi;

I got a slightly different answer, but I have confirmed mine.

## #14 Help Me ! » Olympiad mathematical problems » 2016-07-28 11:50:26

Mathegocart
Replies: 11

If 5/8 of the kids ahead of john and 1/5 of the kids behind John totals the same as the number of kids on the Merry Go Round, how many kids are on the Merry Go Round?
Hint: On a merry go round, a person is ahead AND behind you at the same time
2) Mr Stars' salary is 1.5 times Thomas' salary. The percentage decrease in S's salary is the same as the increase in T's salary. They now earn the SAME salary. By what percent was S's salary increased?
3) Write 1/2 as the sum of 5 unit fractions. A unit fraction is of the form 1/x, where x is a positive integer
Can someone help me?
4) What is the remainder when 2^100+3^100 is divided by 5?

## #15 Re: Help Me ! » e and ln » 2016-07-28 11:48:29

Zeeshan 01 wrote:

yes and ln how we use it

To expand on bobbym's explanation, ln(e) = 1.
ln(ab) = ln(a) + ln(b)
The derivative of ln(x) is 1/x.
Natural logarithms play a large role in complex numbers, and you will see why.

## #16 Re: Help Me ! » differentiation » 2016-07-28 01:11:36

bobbym wrote:

That is the Leibniz notation for differentiation. When you say work further what do you mean?

I think he assumes dy and dx to be different expressions, and he is asking why can't we simplify dy/dx --> y/x? We do not treat them as different expressions,

## #17 Re: Help Me ! » Helicopter problem » 2016-07-26 10:28:59

bob bundy wrote:

hi Mathegocart

Work back from the available fuel.  6600 to start but 1200 must be kept as reserve and half hour = 600 for the transfer so the helicopter has 6600 - 1200 - 600 = 4800 for its journey.  It must go out and back so it can travel to a point at sea 2400 pounds of fuel away from the hospital = 2 hours of flight time.

In 2 hours the ship will cover 20 miles and the helicopter 300 miles so they won't meet.  That's why the helicopter must wait while the ship gets nearer before taking off.

So wait while the ship travels 80 miles, then set off and meet at a point 300 miles from the hospital.

I'm assuming the two must be stationary during the transfer.  You could shave a bit more off the time if the helicopter can meet the ship, turn around and match its speed while both travel towards the land.  Then once the passenger is aboard the helicopter, it is nearer the hospital so won't take 2 hours to get there.  Can you re-calculate using this interpretation? post back if you want me to try it.

Bob

leave the ship to get to the ship as quickly as possible? We do not go back to the ship and then back to the hospital. We just want to know the time to go to the ship.

## #18 Re: Help Me ! » Helicopter problem » 2016-07-26 10:06:08

bob bundy wrote:

hi Mathegocart

Work back from the available fuel.  6600 to start but 1200 must be kept as reserve and half hour = 600 for the transfer so the helicopter has 6600 - 1200 - 600 = 4800 for its journey.  It must go out and back so it can travel to a point at sea 2400 pounds of fuel away from the hospital = 2 hours of flight time.

In 2 hours the ship will cover 20 miles and the helicopter 300 miles so they won't meet.  That's why the helicopter must wait while the ship gets nearer before taking off.

So wait while the ship travels 80 miles, then set off and meet at a point 300 miles from the hospital.

I'm assuming the two must be stationary during the transfer.  You could shave a bit more off the time if the helicopter can meet the ship, turn around and match its speed while both travel towards the land.  Then once the passenger is aboard the helicopter, it is nearer the hospital so won't take 2 hours to get there.  Can you re-calculate using this interpretation? post back if you want me to try it.

Bob

Thank you, bundy, but I do not clearly get the answer. Would it be 1:30 PM?

## #19 Help Me ! » Square coordinate problem » 2016-07-26 09:32:10

Mathegocart
Replies: 2

1. One diagonal of a square lies on the y axis of a coordinate system. The coordinates of 1 corner is 3,7. What are the coords of the opposite corner?

## #20 Help Me ! » Confirmation of problem » 2016-07-26 08:00:26

Mathegocart
Replies: 1

A painter has 4 colors and a box. He wishes to paint the inside in 1 color and the outside in another color. How many ways are there to color it?
Is it 12?

## #21 Re: Help Me ! » angles » 2016-07-26 04:59:06

I am going to interpret that you are saying "why do we use radians instead of angles in trigonometry?"
Welll many trig functions have many characteristics(periods,allowed values, etc) that make radians particularily handy.
Look, which looks more convenient? Radians....or degrees?

The number pi, as strange as it seems, is at the heart of mathematics. The number 360 isn't. Clinging to 360 instead of pi will not allow you to see the beauty of trigonometry.
Let's just start with any old circle and wrap the radius of the circle around the circle.

See how it forms a angle? We'll call that a RADIAN.
Now, let’s take that radius and wrap it around the outside of the circle. See how it forms an angle? We’ll call that angle 1 radian.

Now we have fit nearly 6 radians in

There's a little bit remaining.
We get
C = 2πr.
There are exactly 2pir radians in a circle!

## #22 Help Me ! » Helicopter problem » 2016-07-25 09:28:49

Mathegocart
Replies: 6

You are a pilot of a medical evacuation helicopter. At 5:30 am, you receive word that a passenger  on a ship fell ill and needs to be airlifted as quickly as possible to the nearest hospital, which is where you and the helicopter are located. The cruise ship is 400 miles away from you, where the nearest hospital is found. The ship is making it's way at 10 mph to your port. Your helicopter only has 6600 pounds of fuel, and it burns 1,200 pounds of fuel every hour when it is airborne. Airlifting a passenger takes 30 minutes. Federal law mandates that pilots most retain an hours worth of fuel at all times. If your helicopter travels at 150 miles per hour, at what time must you leave the ship to get to the ship as quickly as possible?
This was one of my practice HW problems and the answer is apparently not 5:30.AM
Could someone give me a detailed explanation on why this isn't 5:30 AM and what the answer is?
THOUGHT PROCESS;
The helicopter can obviously not travel for more than 5 hours since it must maintain an hours worth of fuel.
Now the heli and boat have a 400 mile distance between eachother.
x = time since 5:30 AM
y = time after 5:30 AM when starting the helicopter
now the helicopter's traveled distance is 150(x-y), and the boat's distance is 10x. Summing these expressions, we get 160x-150y = 400, which is (16/15)x- 40/15.
Getting to the ship as quick as possible is minimizing both x and y, and I got 2.5,0.
So is it 8:00 AM?

## #23 Re: Exercises » Exponent Slash, #1 » 2016-07-21 02:12:24

6 also is a solution, and 6 is not a cube. $\frac{6!}{6^{2}}$ = 20

## #24 Re: Exercises » Exponent Slash, #1 » 2016-07-21 02:10:10

bobbym wrote:

Hi;

Both answers are reasonable solutions, also thickhead has a good soultion as well.