Mathematical expressions are a combination of numbers, variables (like x, y, or z), and operators (like +, −, ×, and ÷) that represent a particular value or quantity. For example, 2+3 is a simple mathematical expression. The + is an operator that tells us to add the two numbers together.

The expression 90−10+20 is a combination of subtraction and addition operations.

Start with the number 90. This is your initial quantity. Then, subtract 10 from 90. When you subtract 10 from 90, you are taking away 10 from the initial quantity. So, 90−10=80. Finally, add 20 to the result. When you add 20 to 80, you are increasing the quantity by 20. So, 80+20=100.

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