Cross-Curricular Mathematics: porcentajes en situaciones cotidianas

Ejemplo

I traveled to Argentina and bought a pair of shoes there. I paid $250 for them. Then, I realized that here in Chile they were 40% cheaper. How much do the shoes cost in Chile?

1. El precio en Argentina, $250, representa el 100% del costo.
2. Como en Chile son 40% más baratos, se calcula el 40% de 250 mediante regla de tres: \frac{250 \times 40}{100}.
3. Se multiplica: 250 \times 40 = 10\,000.
4. Se divide por 100: 10\,000 \div 100 = 100.
5. Se resta el descuento al precio original: 250 - 100 = 150.

I went to a café with my best friend. We wanted to have a cappuccino and a sandwich. In total, the bill cost $32. I thought that it was too expensive, but my friend told me that in another café a cappuccino with a sandwich cost 65% more, so we stayed there. How much do the cappuccino and the sandwich cost in the other café?

1. El costo en la cafetería actual, $32, representa el 100%.
2. En la otra cafetería cuesta 65% más, es decir, 100\% + 65\% = 165\% del precio actual.
3. Se plantea la regla de tres: \frac{32 \times 165}{100}.
4. Se multiplica: 32 \times 165 = 5\,280.
5. Se divide por 100: 5\,280 \div 100 = 52{,}8.

Today, the president announced that the price of a subway ticket is going to increase 32% next week. Currently, the subway ticket price is $16. How much is the subway ticket going to cost next week?

1. El precio actual, $16, representa el 100%.
2. Con el aumento del 32%, el nuevo precio será 100\% + 32\% = 132\% del precio actual.
3. Se plantea la regla de tres: \frac{16 \times 132}{100}.
4. Se multiplica: 16 \times 132 = 2\,112.
5. Se divide por 100: 2\,112 \div 100 = 21{,}12.