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Lesson · Grade 7 · Mathematics

Evaluating an Expression by Substitution

  • Grade 7
  • Mathematics
  • 1 min 1 s
  • British Columbia
  • BC7-MA-36

To find the value of 4n + 7 when n = 5, the video first shows that 4n means 4 × n, then swaps the 5 into the letter's place to get 4 × 5 + 7, and points out that this is not 45. It multiplies before adding (4 × 5 = 20, then 20 + 7 = 27) and ends on the recap: replace the letter, then work it out in order.

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In one sentence

The question this lesson answers

What is the value of 4n plus 7, when n equals 5?

To evaluate an expression means to find its value.

Transcript

What the lesson says

What is the value of 4n plus 7, when n equals 5?

To evaluate an expression means to find its value.

The letter n stands for a number, and here n is 5.

A number beside a letter means multiply, so 4n means 4 times n.

To substitute, replace n with 5.

Keep the times sign, so it is 4 times 5, not 45.

Now follow the order of operations, so multiply before you add.

4 times 5 is 20.

Then 20 plus 7 is 27.

So when n is 5, 4n plus 7 equals 27.

To evaluate, replace the letter with its value, then follow the order of operations.

Curriculum

Where this fits

British Columbia, Grade 7

Mathematics, Patterns and algebra: discrete linear relations, using expressions, tables, and graphsBC7-MA-36

Previous: Finding the rule from a tableNext: Graphing a Linear Relation from Its Table

The outcomes and strands follow the British Columbia curriculum.

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