How much costs some unknown quantity of the product, if we know the price for other quantity? Let’s calculate the price for the volume B in proportion to the known value of the volume A.

Examples of calculations of direct proportionality:

• How much costs 100 pounds of potatoes, when it’s known that bag of 5 lbs costs $4.41?
• What is the price should be for 0.5 liter bottle of vodka, if 0.7 liter bottle costs $12.53 (Example of calculation)
• Or cost of the half liter of vodka, if minimal government-regulated retail price for 1 liter of 100% spirit is $16.1? (Example of calculation)
• But here is about time, not money... If the train passes 420 miles per 3 hours and 15 minutes (3 and a quarter hours), how long will it take to drive 520 miles? (Example of calculation, where result is the number of hours.)

Inverse proportionality:

• Bottle of 0.5l of vodka costs 89.4 ₴. And we have 1000 ₴. How much liters of vodka (liters, not bottles) can we buy with our budget? (Example of calculation). In the real life task the result should be rounded down to the nearest integer.)
• If 2 mowermans can mow a meadow in 10 days, how long it takes for 10 mowermans?
• If 2 programmers can make an app in 10 days, how long will it take for 10 programmers? (Example )
• If 1 woman can carry a baby durin 9 months, how long will it take for 9 women?

TODO: Ещё здесь будет позже:

• Пропорция трёх множителей — 3 грузовка перевозят 300 тонн груза за 3 дня. Сколько перевезут груза 5 грузовиков за 7 дней?
• Пропорциональное распределение — на примере нескольких барменов, которые работают разное количество времени, получая процент от прибыли заведения.