50 birds were resting on two trees. 5 birds from the first tree flew away. Another 15 birds from else where flew to the second tree. The number of birds on the second tree was 3 times as many as the number of birds on the first one. How many birds were on each tree at first?

Answer 1

to start,
x+y = 50
after the migrations,
y+15 = 3(x-5)
Now just solve for x and y

Answer 2

x=32 y=18