Problem
(7) In a barn there are 17 animals. Some are cows and some are ducks. There are 54 legs in all. Which system of equations below could be used to find how many cows and how many ducks are in the barn? (A) \( c+d=17 \) (B) \( c+d=54 \) \( 4 c+2 d=54 \) \( 4 c+2 d=17 \) (C) \( c+d=17 \) (D) \( c+d=17 \) \( 2 c+4 d=54 \) \( 4 c+2 d=6 c d \)
Solution
Step 1 ：\(c + d = 17\)
Step 2 ：\(2c + 4d = 54\)
