How many legs?

• Jan 15th 2011, 04:30 AM
Natasha1
How many legs?
I had a question in a test the other day, which I couldn't work out. It sounds relatively trivial, but I just couldn't do it.

It went like this...

In a farm there are 16 animals which are made up of rabbits and chickens only. We know there are 42 legs altogether.

How many chickens and rabbits are there?

This is my version but it took me nowhere...

chicken = 2 legs
rabbits = 4 legs

2X + 4X = 42 so 6X = 42 and X = 7

So 7 chickens and 7 rabbits... but we need 16 animals altogether???? Need help please.
• Jan 15th 2011, 04:35 AM
Also sprach Zarathustra
There two variables x and y.

The equations are:

(1) 2x+4y=42
(2) x+y=16
• Jan 15th 2011, 04:37 AM
Natasha1
ahhhh yes.

so y = 5 and x = 11
• Jan 15th 2011, 04:39 AM
Also sprach Zarathustra
Yes!

11 chickens and 5 rabbits.
• Jan 15th 2011, 04:39 AM
Natasha1
Thank you!
• Jan 15th 2011, 06:19 AM
Quote:

Originally Posted by Natasha1
I had a question in a test the other day, which I couldn't work out. It sounds relatively trivial, but I just couldn't do it.

It went like this...

In a farm there are 16 animals which are made up of rabbits and chickens only. We know there are 42 legs altogether.

How many chickens and rabbits are there?

This is my version but it took me nowhere...

chicken = 2 legs
rabbits = 4 legs

2X + 4X = 42 so 6X = 42 and X = 7

So 7 chickens and 7 rabbits... but we need 16 animals altogether???? Need help please.

When you write 2X+4X=42,

you are inadvertently exclaiming that the number of rabbits equals the number of chickens
(if both numbers is X).

Remember, 2 unknowns is solved with 2 clues (equations),
3 unknowns is solved with 3 seperate clues,
1 unknown only requires 1 clue etc.
• Jan 15th 2011, 06:21 AM
Natasha1
Yes yes. I have noticed my mistake now. Thanks