Math help

2007-05-30 17:20:13

#1

theit57: I am THE Frodo Baggins.; +124|6863|6 feet under

Can someone please help me with these (peferably with work and not just the answer) couple problems becuase a couple of my friends and i don't get how to do them:

1. Elena has a 3-digit combination lock on her gym lock and has forgotten the combination. if she knows that the first digit is 3 and the second is prime, how many numbers must Elena try before the lock is sure to open?

answers are: 30, 12, 40, 120

2. A bag contains 3 green marbles and 7 2 marbles are drawn at random. one marble is drawn and not replaced. then a second is drawn and not replaced. what is the probability that the first is yellow and the second is green.

answers are: 7/3, 7/90, 7/30, 1/7

3. A drawer contains 5 red socks, 8 white socks, and 2 blue socks. without looking, you draw out a sock and draw a second sock w/o returning the first sock. what is the probability that the first sock and the second sock are both white?

answers are: 4/15, 2/21, 1/9, 64/225

I honestly have no clue how to do these, so any help would be appreciated. thanks.

2007-05-30 17:24:08

#2

David.P: Banned; +649|6738

On number one how many numbers does the lock go up to? 0-10? Or 1-38 which is popular on many padlcoks.

2007-05-30 17:31:36

#3

theit57: I am THE Frodo Baggins.; +124|6863|6 feet under

David.Podedworny wrote:
On number one how many numbers does the lock go up to? 0-10? Or 1-38 which is popular on many padlcoks.

i think that it goes 0-9 because it says second digit

Last edited by theit57 (2007-05-30 17:45:35)

2007-05-30 17:31:41

#4

derstralle: Iron Egg Skill, bitches!; +29|6680

theit57 wrote:
3. A drawer contains 5 red socks, 8 white socks, and 2 blue socks. without looking, you draw out a sock and draw a second sock w/o returning the first sock. what is the probability that the first sock and the second sock are both white?

You have a total: 5 red socks + 8 white socks + 2 blue socks = 15 socks in the drawer.
The probability that your first sock is white is therefore 8/15.
After that you have 14 socks in it of which 7 are white.. therefore the second probability is 7/14.
If you multiply these two numbers you get the probability of drawing a pair of white socks:
7/14*8/15=8/30=4/15

Maybe I'll add the other answers later... But if you get this concept I am sure you will be able to solve the others by yourself.

2007-05-30 17:46:05

#5

David.P: Banned; +649|6738

theit57 wrote:
David.Podedworny wrote:
On number one how many numbers does the lock go up to? 0-10? Or 1-38 which is popular on many padlcoks.
i think that it goes 0-9 because it says second digit

1-9 or 0-9? I need to know since i think i have an answer but its too much.

EDIT: Do you count 1 as a prime number? If you do then the answer is 60 if you dont then the answer is 40. Dont put that down yet! Gimme time to think.

Last edited by David.Podedworny (2007-05-30 17:49:19)

2007-05-30 17:48:46

#6

theit57: I am THE Frodo Baggins.; +124|6863|6 feet under

David.Podedworny wrote:
theit57 wrote:
David.Podedworny wrote:
On number one how many numbers does the lock go up to? 0-10? Or 1-38 which is popular on many padlcoks.
i think that it goes 0-9 because it says second digit
1-9 or 0-9? I need to know since i think i have an answer but its too much.

0-9

2007-05-30 17:56:22

#7

David.P: Banned; +649|6738

0-9 then its like this.

2,3,5,7 - 0,1,2,3,4,5,6,7,8,9

321 322 323 324 325 326 327 328 329 320| 331 332 333 334 335 336 337 338 339 330| 351 352 353 354 355 356 357 358 359 350| 371 372 373 374 375 376 377 378 379 370| multiply by 10 = 40. The answer to #1 is 40. (My mind works in weird ways, Thats why get half on math tests usaully)

In other words just multiply 4 the amount of prime numbers by 10 the amount of numbers on a lock.

Last edited by David.Podedworny (2007-05-30 17:58:45)

2007-05-30 18:01:03

#8

theit57: I am THE Frodo Baggins.; +124|6863|6 feet under

1. 40 (# of prime before 10) X 10 (0-9)

thats what i think along with some of my friends

2007-05-30 18:02:05

#9

theit57: I am THE Frodo Baggins.; +124|6863|6 feet under

David.Podedworny wrote:
0-9 then its like this.

2,3,5,7 - 0,1,2,3,4,5,6,7,8,9

321 322 323 324 325 326 327 328 329 320| 331 332 333 334 335 336 337 338 339 330| 351 352 353 354 355 356 357 358 359 350| 371 372 373 374 375 376 377 378 379 370| multiply by 10 = 40. The answer to #1 is 40. (My mind works in weird ways, Thats why get half on math tests usaully)

In other words just multiply 4 the amount of prime numbers by 10 the amount of numbers on a lock.

i was just about to put 40, i was typing it, no fair

2007-05-30 18:02:28

#10

Ryan: Member; +1,230|7308|Alberta, Canada

lolwut

2007-05-30 18:06:54

#11

BolvisOculus: Spagett!; +167|7084|Manitowoc, WI

OK, who the hell remembers that the second number on their lock combination is prime.

2007-05-30 18:07:47

#12

theit57: I am THE Frodo Baggins.; +124|6863|6 feet under

BolvisOculus wrote:
OK, who the hell remembers that the second number on their lock combination is prime.

dunno

2007-05-30 18:09:52

#13

David.P: Banned; +649|6738

theit57 wrote:
David.Podedworny wrote:
0-9 then its like this.

2,3,5,7 - 0,1,2,3,4,5,6,7,8,9

321 322 323 324 325 326 327 328 329 320| 331 332 333 334 335 336 337 338 339 330| 351 352 353 354 355 356 357 358 359 350| 371 372 373 374 375 376 377 378 379 370| multiply by 10 = 40. The answer to #1 is 40. (My mind works in weird ways, Thats why get half on math tests usaully)

In other words just multiply 4 the amount of prime numbers by 10 the amount of numbers on a lock.
i was just about to put 40, i was typing it, no fair

Hey man you gotta have a brain like me sometimes to think that fast(Really you dont i have adhd on a level never seen before and homocidal tendencies towards assholes.)

2007-05-30 18:20:59

#14

nukchebi0: Пушкин, наше всё; +387|6789|New Haven, CT

On number two, just multiple the probability of drawing a yellow by the probability of drawing a yellow marble with 10 total marbles by the probability of drawing a green marble with 9 total marble (7/10*3/9=21/90=7/30).

2007-05-30 18:28:45

#15

dill13: Member; +67|6658

1. i dont know why you think otherwise but 1,2,3,5,7 are the prime numbers before 10 making the answer 50 unless the teach it wrong in the states or something cause they dont have the right answer.
2. 7 yellow out of 10 or 7/10 times 3 green out of nine since your missing a yellow one or 3/9
7/10x3/9 or 7/10x1/3=7/30
follow derstralle for number three

2007-05-30 19:04:35

#16

theit57: I am THE Frodo Baggins.; +124|6863|6 feet under

maybe the last one:
{0,1,2,3,4,5,6,7,8,9,10}

what is the probability that one of the numbers chosen at random is a solution to 3X + 1 < 13

2007-05-30 19:08:13

#17

nukchebi0: Пушкин, наше всё; +387|6789|New Haven, CT

Find the solutions to the inequality, quantify them, and then divide by eleven.

In this case, x<4 solves the problem (assuming integers only). You have four of the ten integers which solve the problem correctly, thus the probability is 4/11.

Last edited by nukchebi0 (2007-05-30 19:12:02)

2007-05-30 19:48:46

#18

theit57: I am THE Frodo Baggins.; +124|6863|6 feet under

last couple:

1. ((X+5)/(X-5))/((X+5)(X-5)/(5-X))
answers are: (X+5)/(X-5), 1/(5-x), 1/(3-X), 1/(X-5)

2. ((X+3)/(X+4)(X-3)) - (X+4)/(X-3)(X+3)
answers are: (-2x-7)/((X+4)(X+3)(X-3), same except that it minus 4 on the bottom, -(1)/(X+4)(X-3)(X-3), same except that its minus 4

3. ((((4)/(X))-((1)/(3X)))/((1)/((3X))/((3)/(2X))))

4. (-x^2-x+2)/(1-x)

5. (((x-6)(x+6))/(x+5))/(x+6)

Last edited by theit57 (2007-05-30 19:52:44)

2007-05-30 19:49:18