Adam has a total of 11 ducks and donkeys.
The difference in their number of legs is 4.
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 |
11 |
11 x 2 = 22 |
0 |
0 x 4 = 4 |
22 - 0 = 22 |
10 |
10 x 2 = 20 |
1 |
1 x 4 = 4 |
20 - 4 = 16 |
8 |
8 x 2 = 16 |
3 |
8 x 4 = 12 |
16 - 12 = 4 |
If all of the animals are ducks,
the number of legs needed
= 11 x 2
= 22
Total difference in the number of legs
= 22 - 4
= 18
Difference in the number of legs when 1 duck is replaced by 1 donkey
= 22 - 16
= 6
Number of donkeys
= 18 ÷ 6
= 3 (a)
Number of ducks
= 11 - 3
= 8 (b)
Answer(s): (a) 3; (b) 8