Question

Find the number of ways in which all 12 letters of the words REFRIGERATOR can be arranged if the Rs must all be together.

Answer 1

R - 4
E - 2

Answer 2

@experimentX sorry it was about permutations and combinations :P

Answer 3

yeah ... first find out the repeating terms. i'm bad with observation :(

Answer 4

yeah I did that...I did 4! X 9! but the answer is 9!/2! which I really don't understand.

Answer 5

If the R's must be together, just take out one R. Then, you have one less letter.

Answer 6

*2 less letters

Answer 7

Next, find the other letters, if any, that repeat. Can you tell me the answer?

Answer 8

the answer is 9!/2! = 181 440

Answer 9

@Natshane , I can explain the answer, but you must look at what I've already said.

Answer 10

okay, but why do we have to take out 2Rs?

Answer 11

REFRIGERATOR
-> since the R's must be together, we can actually ignore the other two Rs.

Answer 12

If you think about it RRRFIGEATO is really just taking out the other 2 Rs and putting them where the third R is. Thus we can take out 2 of the Rs

Answer 13

oh yeah, that makes sense..

Answer 14

Sorry, 3 of the R's. @inkyvoyd was never the best speller.

Answer 15

as its said R must be together so taking 4 R as 1,the total arrangement would be 9! and then 2 E are being repeated in thiis case too we will write (9!/2!)

Answer 16

Anyways, we are left with 9 letters: Now, the job is to figure out which ones repeat.

Answer 17

OMG LANA YOU TROLL ME

Answer 18

Besides the R, we have 2 repeating E's.

Answer 19

Haha! that actually make sense! thank you guys for the help!

Answer 20

8! + 4 ?

Answer 21

the answer is 9!/2!, yup this question had me thinking a lot..