A man borrows 40,000 on a short term loan and is charged interest of 1naira on each 10naira per week. How much does he pay back altogether, if he borrows the money for 3 weeks?

First, we need to calculate how much interest the man will pay each week for the 40,000 loan:

1 naira interest on each 10 naira loaned means 1 naira interest on every 10 naira borrowed.

So, for a 40,000 loan, the interest per week will be:
40,000 / 10 = 4,000 naira

Thus, the man will pay 4,000 naira in interest each week for borrowing 40,000 naira.

For a loan period of 3 weeks, the total interest paid will be:
4,000 naira x 3 weeks = 12,000 naira

Therefore, the man will pay back a total of:
40,000 naira (loan) + 12,000 naira (interest) = **52,000 naira altogether**