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When we substitute a number for a letter, we simply replace the letter with the number.

However, we must remember that 4b means 4 x b.

 

Example

Work out the value of the following expression when a = 0.4

3a - 1

 

Answer

3a - 1

= 3 x a - 1

= 3 x 0.4 - 1

= 1.2 - 1

= 0.2

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