Hannah wants to save $80 for five weeks. In the first week, she saved $4 and she plans to save twice as much as her savings as the previous week. How much will she save in the fifth week to reach her goal? Think carefully first, then make a decision:
In the second week, Hannah will save $4 x 2 = $8. In the third week, she will save $8 x 2 = $16. In the fourth week, she will save $16 x 2 = $32. Her total savings for a month will be $4 + $8 + $16 + $32 = $60. Hannah needs to save $80 - $60 = $20 in the fifth week. So, the answer is 20.