Question: Alex has 4 pens in the first week of a month. Every week her pen collection doubles. How many more pens will Alex have than Jane if Jane will have 16 pens after a month? Think carefully first, then make a decision:
If Alex has 4 pens in the first week of a month, she will have 4 * 2 = 8 pens in the second week. After her pen collection doubles in the third week, Alex will have 2 * 8 = 16 pens. In the last week of the month, Alex will have 2 * 16 = 32 pens after her pen collection. If Jane has 16 pens after a month, Alex will have 32 - 16 = 16 more pens than Jane. So the answer is 16.