A student gives his friends small, short-term loans for periods of 1, 2 or 3 weeks after
which time they must be repald in full. He
always lends on a Friday afternoon. He starts
with €120
and loans
out the following
amounts each week:
week 1:€45
week 2:€25
week 3:€18
week 4:€20

what is the smallest amount of money he has
by the end of the 4th Friday?