Cheaper If You Buy More

"Do you want to buy more? It is cheaper if you buy more.", the young lady managing the makeshift stall selling Chinese New Year goodies outside a 7-11 type store in Singapore promised.

I looked at the sign that shows the price. It states that 100g of the organic nuts cost $3.80 while 500g of the nuts cost $19.

Show, with appropriate calculations, if it is true that it is "cheaper if you buy more".

I bought 100g of the organic nuts to snack on between meals.

This is likely a Primary 4 problem. In Singapore, Primary 4 students are expected to achieve this standard for the unit on money.

multiplication and division of money in decimal notation, • solving word problems involving the 4 operations of money in decimal notation.