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Birds and Beasts

Posted by Karl Sharman on December 23, 2010 – 2:27 pm

Yesterday I met a zookeeper. I asked him how many birds and beasts he had in his zoo. He told me that there were 30 heads and 100 feet in his zoo. How many birds and beasts does he have, assuming that all birds have two feet and all beasts have 4 feet?

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This post is under “Tom” and has 21 respond so far.

21 Responds so far- Add one»

1. 1. Jennifer Said：

30..?

2. 2. Wizard of Oz Said：

20 beasts and 10 birds (assuming none of the birds are dressed ready for stuffing, roasting and consuming for Christmas dinner).

3. 3. Ashish Said：

X=Beast
Y=Birds

x+y=30
4x+2y=100

X=20
Y=10

Agree with Wiz…

Sometimes it feels good to solve small small things considering you haven’t done it for long time.

4. 4. Random Guy Said：

For those who dont get Ashish’s explanation:

x+y=30
So 2x+2y=60

Since 4x+2y=100, we can take 100-60=2x=40

Therefore x=40/2=20 and y=30-20=10

5. 5. Karl Sharman Said：

Looks like Christmas has come real early for Wizard, Ashish and Random Guy with such an easy puzzle. Still, hope you will try harder and get the right answer….

6. 6. Wizard of Oz Said：

Is the zookeeper including himself? If so, 9 birds and 20 beasts.

7. 7. Karl Sharman Said：

The zoo-keeper may consider himself a beast in his own mind, but for the sake of this puzzle, no, he is not numbered amongst beast or fowl.

8. 8. tony Said：

none

9. 9. xoxoHamoxoxo Said：

that is umm 2o beasts and 10 birds

10. 10. Appu Said：

20 beasts
10 birds

11. 11. Chris Said：

Katl, I think you’re doing a wind-up.

Merry Christmas.

12. 12. Karl Sharman Said：

Nope, no wind up… Jennifer scores first. It is an easy maths question to find the number of birds and the number of beasts, which distracts from the question… How many birds and beasts does he have…..

Wizard of Oz certainly got the numbers of each type of animal.

Maybe I should have posted this as a ToM rather than Maths

13. 13. tutu Said：

10 birds and20 beasts

14. 14. Euclid's Brother Said：

I guess I did it the hard way:

f = fowl (birds)
b = beasts

f + b = 30
2f + 4b = 100

4b = 100 – 2f
b = (100-2f)/4
b = 25 – f/2

f + 25 – f/2 = 30
f – f/2 = 5
f/2 = 5
f = 10

10 + b = 30
b = 20

fowl = 10
beasts = 20

15. 15. DP Said：

Being Christmas, my in-laws are in town right now. My father-in-law came up with this other method of solving it.
He said out loud “well 30 beasts would make 120 legs, so 20 beasts and 10 birds”.
the logic being that if there were 30 beasts, you would get 30*4=120 legs. 120-100=20. since each time you take away a beast and replace with a bird, you essentially take away 2 legs, while maintaining the head count. you need to take away 20 legs, and since each bird has 2 legs, 20/2=10 birds. subtracting for the total, 30-10=20 beasts.

4x+2y=100
x+y=30
=======>>
x=20
y=10

17. 17. Mandy Said：

who cares about the feet. there are 30 heads…assuming they all have heads…there are 30 birds and beasts

18. 18. sara Chainwater Said：

51 of the 100 are birds and 49 of the 100 are beasts but that is all i could work out because i, like most people on this forum are wondering weather the zoo keeper is included in the beast category? If you could kindly reply to my message or comment on it letting me know weather the zookeeper is included in the beast category that would be wonderful.
Posted by Sara chainwater

19. 19. Karl Sharman Said：

Hi Sara,