Question: Jim has 2 rows of 4 trees to start. When he turns 10 he decides to plant a new row of trees every year on his birthday. On his 15th birthday after he doubles the number of trees he has. How many trees does he have? Think carefully first, then make a decision:
He started with 2 * 4 = 8 trees. He plants trees for 15 - 10 = 5 years. So he planted 5 * 4 = 20 trees. So he had 20 + 8 = 28 trees. After doubling them he had 28 * 2 = 56 trees. So the answer is 56.