A barn contains cows, ducks, and a 3-legged dog named Tripod. There are twice as many cows as ducks

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A barn contains cows, ducks, and a 3-legged dog named Tripod. There are twice as many cows as ducks in the barn and a total of 313 legs. How many ducks are there in the barn?

• Let the number of ducks be d. Duck legs = 2 * d = 2d
• Number of cows = 2d. Cow legs = 4 * 2d = 8d
• 1 dog Tripod has 3 legs

Total legs:
2d + 8d + 3 = 313

Solve for d in the equation 2d + 8d + 3 = 313

Step 1: Group the d terms on the left hand side:
(2 + 8)d = 10d

Step 2: Form modified equation
10d + 3 = + 313

Step 3: Group constants:
We need to group our constants 3 and 313. To do that, we subtract 3 from both sides
10d + 3 - 3 = 313 - 3

Step 4: Cancel 3 on the left side:
10d = 310

Step 5: Divide each side of the equation by 10
10d/10 = 310/10
d = 31

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