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Donna 
bought a notebook for $3.50 and then spent half of her remaining money for a textbook.
Next she bought sheet music for $4 and then spent half of the remaining money on a calculator.
She has $8 left. How much money did she start with?
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It is a nice problem to solve it in the backward manner.
Make the sheet of her purchases, step by step:
1. bought a notebook for $3.50
2. spent half of her remaining money for a textbook
3. bought the sheet music for $4.
4. spent half of the remaining money on a calculator.
5. she has $8 left.
Now we will move from the bottom to the top.
- before step 4, she had twice $8, i.e 16 dollars.
- before step 3, sha had 16 + 4 = 20 dollars.
- before step 2, she had twice $20, i.e. 40 dollars.
- before step 1, she had 40 + 3.50 = 43.50 dollars.
It is what she started with.
You may check that my solution and my answer are correct at each step, moving from step 1 to the end.
Solved.
Nice method, isn't it ?
