Bob started out the week with $80. On Monday alone, he spent half the money. On Tuesday, he spent one-fifth of the amount left from Monday. On Wednesday, he spent 3/8ths of the amount left from Tuesday. How much does he have left now? Let's think first. Chain of thought:
On Monday, he spent half of $80 leaving him with $80 - (1 / 2) * $80 = $40. On Tuesday, he spent 1 / 5th of $40 leaving $40 - (1 / 5) * 40 = $32. On Wednesday, he spent 3 / 8ths of $32 leaving $32 - (3 / 8) * $32 = $20.
Therefore, the answer is 20.