A flock of birds was flying around a tree. When they landed, three birds to a branch, no branches were left and one bird had to keep flying around the tree. Then, all the birds took off, flew around the tree again and landed to sit, four to a branch. Now, no birds were left flying but one branch had no birds sitting on it. How many branches were on the tree and how many birds were in the flock?

Answer: 5 branches and 16 birds.

Step-by-step explanation:

If the number of birds is B, and the number of branches is N.

First we have the equation:

B = 3*N + 1

(3 birds per branch + 1 that was flying around)

for the second equation we have:

B = 4 * (N - 1)

(4 birds per branch, but one branch had no birds on it, so there are N - 1 branches used)

now we can write:

3*N + 1 = 4 * (N - 1)

3*N + 1 = 4*N - 4

4 + 1 = 4*N - 3*N

5 = N

So we had 5 branches, now we can replace it in one of the equations and find the number of birds.

B = 3*N + 1 = 3*5 + 1 = 16