Adam has a total of 12 ducks and donkeys.
The difference in their number of legs is 12.
How many (a) donkeys and (b) ducks does Adam have?
Number of ducks |
Number of ducks' legs |
Number of donkeys |
Number of donkeys' legs |
Difference in the number of legs |
12 |
12 x 2 = 24 |
0 |
0 x 4 = 4 |
24 - 0 = 24 |
11 |
11 x 2 = 22 |
1 |
1 x 4 = 4 |
22 - 4 = 18 |
10 |
10 x 2 = 20 |
2 |
10 x 4 = 8 |
20 - 8 = 12 |
If all of the animals are ducks,
the number of legs needed
= 12 x 2
= 24
Total difference in the number of legs
= 24 - 12
= 12
Difference in the number of legs when 1 duck is replaced by 1 donkey
= 24 - 18
= 6
Number of donkeys
= 12 ÷ 6
= 2 (a)
Number of ducks
= 12 - 2
= 10 (b)
Answer(s): (a) 2; (b) 10