Adam has a total of 14 ducks and cows.
The difference in their number of legs is 4.
How many (a) cows and (b) ducks does Adam have?
Number of
ducks |
Number of
ducks' legs |
Number of
cows |
Number of
cows' legs |
Difference in the
number of legs |
| 14 |
14 x 2 =
28 |
0 |
0 x 4 =
4 |
28 - 0 =
28 |
| 13 |
13 x 2 =
26 |
1 |
1 x 4 =
4 |
26 - 4 =
22 |
| 10 |
10 x 2 =
20 |
4 |
10 x 4 =
16 |
20 - 16 =
4 |
If all of the animals are ducks,
the number of legs needed
= 14 x 2
= 28
Total difference in the number of legs
= 28 - 4
= 24
Difference in the number of legs when 1 duck is replaced by 1 cow
= 28 - 22
= 6
Number of cows
= 24 ÷ 6
= 4 (a)
Number of ducks
= 14 - 4
= 10 (b)
Answer(s): (a) 4; (b) 10
