# Proportionality

The ratio, or quotient, of direct proportionality is always constant

where *k* is constant. This means that as one grows, the other will grow at the same proportion.

**Example 1**

Liisa-Petter had 280 sea cucumbers. They eat 3.5 kg of phytoplankton daily. Liisa-Petter wanted to buy 140 more sea cucumbers for her farm. How much phytoplankton does she need to reserve for all the sea cucumbers per day?

**Solution**

There is a direct correlation between the amount of sea creatures and the amount of food consumption. So we can say that they are directly proportional.

Let's find the proportion and solve *x*

Answer: About *5.3 kg* of phytoplankton should be reserved per day.

The product of an inverse proportionality is also always constant.

where* k* is constant. This means that as one grows, the other will shrink in the same proportion.

**Example 2**

Liisa-Petter noticed that the balance in her bank account was inversely proportional to the hours spent at the pub. If she sat in the pub for 5 hours then there was only €200 left in her account. She wanted to sit for an additional 3 hours because the music was so good and the drinks were, of course, cheap. How much money is in the account when Liisa-Petter leaves home?

**Solution**

Let's make a proportion table

Let form a proportion so that the relation is inverted. That is, the ratio of* x* to *200 *is equal to the ratio of* 5* to *8.*

There is* *€*125* left in the bank account.

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