Once there was a hunch-backed shopkeeper. And he told the following story:
(For readers at grade 6/7 level and up)
“Once I lent 100 dinars, 50 to a sheik from Medina and another 50 to a merchant from Cairo.
“The sheik paid the debt in four instalments, in the amount 20, 15, 10 and 5. .. .. Note that the total of his debt balance is 50 dinars.
| 1st Installment: Paid | 20 | & Still Owe | 30 |
| 2nd installment: Paid | 15 | & Still Owe | 15 |
| 3rd Installment: Paid | 10 | & Still Owe | 5 |
| 4th Installment: Paid | 5 | & Owe | 0 |
| Total Paid | 50 | & Total Owe | 50 |
“Meanwhile the merchants from Cairo also paid the debt of 50 dinars in four instalments, in the following amount: 20, 18, 3 and 9. And here is the balance sheet for his debt.
| 1st Installment: Paid | 20 | & Still Owe | 30 |
| 2nd installment: Paid | 18 | & Still Owe | 12 |
| 3rd Installment: Paid | 3 | & Still Owe | 9 |
| 4th Installment: Paid | 9 | & Owe | 0 |
| Total Paid | 50 | & Total Owe | 51 |
“But note his total owed is 51 dinars”, remarked by the hunchbacked shopkeeper; apparently this should not have occurred.
Using a bit math, can you help our shopkeeper to solve the mystery?
Think on your own first!
Then you might want to take a look at our explanation. Do you agree with us?