Some ducks and cows are in a farm. These animals have a total of 21 heads and 66 legs.
- How many cows are there?
- How many ducks are there?
Number of cows |
Number of cows' legs |
Number of ducks |
Number of ducks' legs |
Total legs |
21
|
21 x 4 = 84 |
0
|
0
|
84 |
20
|
20 x 4 = 80 |
1
|
1 x 2 = 2 |
82
|
12 |
12 x 4 = 48 |
9
|
9 x 2 = 18 |
66
|
Number of legs if all are cows
= 21 x 4
= 84
Big difference between the number of legs of the cows and the ducks
= 84 - 66
= 18
Small difference between the number of legs of one cow and one duck
= 4 - 2
= 2
Numbers of ducks
= 18 ÷ 2
= 9
(b)
Number of cows
= 21 - 9
= 12
Answer(s): (a) 9; (b) 12