# What is an equation ? Definition and examples

An equation is a mathematical sentence stating that two quantities or math expressions are equal.  Notice how the weight on the left is equal to the weight on the right.

We use an equal sign between two quantities or math expressions in order to show that they are equal.

For example, 5 kg  + 2kg = 4kg + 3kg is the equation for the situation above.

1 quarter + 2 dimes  = 2 quarters - 1 nickel is another example of an equation.

An equation can also have missing numbers. When there are missing numbers, we use symbols to represent these missing numbers.

For example, in the equation 9 + ? = 15, ? is the missing symbol

By the same token, in the equation y  × 4 = 24, y is the missing symbol.

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