Answer:
There are 9 llamas.
Explanation:
For Billy, we have to find a number that is divisible by four, because he has one group of lambs, and 3 times as many llamas, which gives us 4 groups altogether. The number must be below 10 in order to not go above 17 when Milly's number of animals are included, but above 4 itself in order to reach the target of 17 in the first place.
As you can guess, the only number that fits all the criteria is 8. It's divisible by 4 and below 10, but above 4 itself.
If Billy has three times as many llamas as lambs, then he must have 2 lambs, and 6 llamas, as 2 × 3 = 6.
If we know that Billy has 8 animals, then we also know that Milly must have 9 animals, as 17 - 8 = 9.
We also know that Milly has 3 groups of animals; one group of llamas, and two groups of lambs, meaning we divide the number of animals she has by 3.
9 ÷ 3 = 3.
This tells us Milly has just 3 llamas, because 3 is one group of 9, and 3 × 2 = 6, because she has twice the amount of lambs.
Billy has 2 lambs and 6 llamas.
Milly has 6 lambs and 3 llamas.
The amount of lambs is irrelevant to our final answer, so we can disregard them and do a final sum of 6 + 3 = 9, which gives us our answer.