Answer:
6 ducks and 13 horses
Step-by-step explanation:
Let H and D be the numbers of Horses and Ducks, respectively.
We are told that:
H + D = 19
Our biology book confirms that:
1 horse = 4 legs, and
1 duck = 2 legs
[In most cases on Earth]
So we can say that:
4H + 2D = 64 legs
Rewrite
H + D = 19 as: H = 19 - D
and then substitute:
4H +2D = 64 legs
4(19-D) +2D = 64 legs
76 - 4D + 2D = 64 legs
-2D = - 12
D = 6 [We have 6 ducks]
Then:
H + D = 19
H + 6 = 19
H = 13 [There are 13 horses]
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Check:
Do 6 ducks and 13 horses have a total of 64 legs?
6*2 + 4*13 = 64?
12 + 52 = 64?
YES
