Are these four cages distinct or identical?
Are the tigers distinct or identical?
THis is from the 2015 perms thread
A zoo keeper wants to place 6 tigers in 4 cages, each can fit a maximum of two tigers.
In how many ways can he place the tigers if no cage to be left empty?
I got
4! x (6C2 x 4C2 x 2C1 x 1C1) = 4320
Because: First Cage: 6C2
Second Cage: 4C2
Third Cage: 2C1
Fourth Cage: 1C1
4! ways to arrange these
Some people got 2160 which is 4320/2
some also got 1080 which is 4320/4
IM confused to what is the right answer. If so why am I wrong
Are these four cages distinct or identical?
Are the tigers distinct or identical?
Last edited by fan96; 6 May 2018 at 1:35 PM.
HSC 2018 - [English Adv.] • [Maths Ext. 1] • [Maths Ext. 2] • [Chemistry] • [Software Design and Development]
_{1}∫^{(3√3)} t^{2} dt cos(3π/9) = log(^{3}√e) | Integral t^{2} dt, From 1 to the cube root of 3. Times the cosine, of three pi over nine, Equals log of the cube root of e.
Assuming the tigers and cages are identical and arranged in a straight line:
If no cage is to be empty and each cage can fit a maximum of two tigers, then there must be either one or two tigers in each cage.
Also, there must be exactly 6 tigers.
The only way to make 6 from adding 1 or 2, four times, is in any order (that sentence is a bit botched but hopefully you get what I mean).
So assuming the cages are identical and they're not arranged in a circle, the problem can be reduced to "How many ways can you arrange two 2's and two 1's?"
Another way to solve the problem is to consider each case by making something similar to a tree diagram.
If the tigers are distinct, multiply the answer by .
If the cages are distinct, multiply the answer by .
Your answer should be correct if the tigers are distinct but the cages are not ().
Last edited by fan96; 6 May 2018 at 1:43 PM.
HSC 2018 - [English Adv.] • [Maths Ext. 1] • [Maths Ext. 2] • [Chemistry] • [Software Design and Development]
_{1}∫^{(3√3)} t^{2} dt cos(3π/9) = log(^{3}√e) | Integral t^{2} dt, From 1 to the cube root of 3. Times the cosine, of three pi over nine, Equals log of the cube root of e.
No I have not
I have heard of it and have seen @fan96 post something about it before,
https://en.wikipedia.org/wiki/Stars_...combinatorics)
Basically if you want to place objects in boxes you can model it using something like
Where the stars are the objects and the bars represent the dividers between boxes. So in the above case you would be placing 6 objects in 3 boxes.
By using the formula for permutations with repetition you can count the number of ways to distribute 6 objects across 3 boxes with no restriction:
,
since there are 6 stars and 2 bars.
It's pretty useful to know but for this question, since the numbers are small and there are quite a few restrictions (no more than 2 tigers in a cage, no cage empty), I don't think it's as useful here. You'd have to subtract the cases where two dividers are together (representing an empty box) and when there are more than two stars next to each other (i.e. more than two lions in a cage).
Last edited by fan96; 6 May 2018 at 4:26 PM.
HSC 2018 - [English Adv.] • [Maths Ext. 1] • [Maths Ext. 2] • [Chemistry] • [Software Design and Development]
_{1}∫^{(3√3)} t^{2} dt cos(3π/9) = log(^{3}√e) | Integral t^{2} dt, From 1 to the cube root of 3. Times the cosine, of three pi over nine, Equals log of the cube root of e.
Can you give me a good question and can you please work it out with this method?
Here's an easier question from one of my school's 4U Task 1 papers:
In how many ways can nine identical rings be placed on the four fingers of the left hand, excluding the thumb, if:
- there are no restrictions?
- there must be at least one ring on each finger?
- there are no restrictions and the rings are all different?
Is that a past HSC question?
HSC 2018 - [English Adv.] • [Maths Ext. 1] • [Maths Ext. 2] • [Chemistry] • [Software Design and Development]
_{1}∫^{(3√3)} t^{2} dt cos(3π/9) = log(^{3}√e) | Integral t^{2} dt, From 1 to the cube root of 3. Times the cosine, of three pi over nine, Equals log of the cube root of e.
fan when there are no restrictions its 220 right?
I used the stars and bars method for it
9 stars 3 bars
12C3
for ii) it is 220 - cases with a finger or till 4 having no rings.
but how do i do it?
HSC 2018 - [English Adv.] • [Maths Ext. 1] • [Maths Ext. 2] • [Chemistry] • [Software Design and Development]
_{1}∫^{(3√3)} t^{2} dt cos(3π/9) = log(^{3}√e) | Integral t^{2} dt, From 1 to the cube root of 3. Times the cosine, of three pi over nine, Equals log of the cube root of e.
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