First, you have to calculate what one American dollar is worth in pesos. 3000 pesos = 270 American dollars, so 3000pesos/270american dollars = 11.1111.... so one American dollar is worth 11.1111... pesos. Calculating how much he has left in American dollars, 100pesos / 11.1111 (1 American dollar in pesos) = 9. He has 9 American dollars.
TIP: You would think it would equal 9.00000000000....1 but since the zeroes go on forever, the one never comes up, which makes it equal to 9.
