A loonie is a $1 coin and a dime is a $0.10 coin. One loonie has the same mass as 4 dimes. A bag of dimes has the same mass as a bag of loonies. The coins in the bag of loonies are worth $400 in total. How much are the coins in the bag of dimes worth?
The bag of loonies are worth $400 in total ⇔ There are 400 loonies in the bag.
But one loonie = 4 dimes in terms of mass, so if the bag of dimes has the same mass as a bag of loonies, then there should be (4)(400) dimes, which is 1600 dimes.
The bag of dimes is worth $1600 (0.10) = $160.