A pattern written as an expression

Use Parthiv's matchstick pattern to write a rule with a letter-number.

Parthiv makes a pattern by placing L shapes side by side. Each L uses 2 matchsticks.

5 Ls need 5 × 2 sticks. 7 Ls need 7 × 2. 45 Ls need 45 × 2. The number changes, but the shape of the answer stays the same.

Say the rule in words first: every L needs 2 sticks, so the number of sticks is 2 times the number of Ls. Make this a habit: words first, then symbols.

Now use a letter for the thing that changes. Let n be the number of Ls. The number of matchsticks is 2 × n.

One expression covers every case. Just put the number in place of n: for n = 45, the sticks needed are 2 × 45 = 90.

Be careful turning words into symbols: 4 more than a number p is p + 4; 4 less than p is p − 4 (not 4 − p!); p less than 4 is 4 − p.

Describe the pattern in words, then replace the changing quantity with a letter-number.

Describe the pattern in words, then use a letter.

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