# Using Given Relations

### Upon studying this section, you should be familiar with the following:

• How to use relationships given in a problem statement to find a desired answer.
• Know when basic physical constants need to be looked up to find a desired answer.

Explanation:

Often, problem statements give relationships that one needs to solve a problem. These relationships are either given directly in the problem statement or need to be looked up.

Relationships given directly:

The relationship between two things are given in the problem statement, no looking up data in table such as density or molecular weight are needed to solve the problem.
The following two examples can simply be solved using the info given in the problem statement.

Example 1:

One customer spends about \$6.50 dollars a meal, how much money would be made on an average Friday night that hosts about 150 customers?

Example 2:

A supersonic aircraft consumes 5320 imperial gallons of kerosene per hour of flight and flies an average of 14 hours per day. It takes roughly seven tons of crude oil to produce one ton of kerosene. The density of kerosene is 0.965 g/cm3. How many planes would it take to consume the entire annual world production of 4.02*109 metric tons of crude oil in one day?

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Looking up Relationships:

In chemical engineering, information in the problem will require addition understanding of the topic to come to an answer. If information about liquid water is given, addition physical properties not given in the problem statement such as the molecular weight or melting point may be needed to solve the problem.

Example 3:

A water tank that provides water to a resort isolated in the mountains holds 10,000 gallons of water. How many water molecules does this correspond to?
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