Problem at the Bank - Solution
A bank customer had $100 in his account.
He then made 6 withdrawals, totaling $100.
He kept a record of these withdrawals, and the balance left in the account, as follows:
| Withdrawals | Balance left |
|---|---|
| $50 | $50 |
| $25 | $25 |
| $10 | $15 |
| $8 | $7 |
| $5 | $2 |
| $2 | $0 |
| $100 | $99 |
So, why are the Totals not exactly right?
There is no reason whatever why the customer's original deposit of $100 should equal the total of the balances left after each withdrawal.
The total of withdrawals in the left-hand column may equal $100, but it is purely coincidence that the total of the right-hand column is close to $100.
Let us show another example, but starting with $200 in the bank:
| Withdrawals | Balance left |
|---|---|
| $50 | $150 |
| $25 | $125 |
| $10 | $115 |
| $8 | $107 |
| $5 | $102 |
| $2 | $100 |
| $100 | $699 |
Moral of this story? Don't Total Balances.
Puzzle supplied by Richard Rider