Cogito
Grade 6 Math · Chapter 5 · Lesson 4
Writing Expressions from Words
Turning a sentence into algebra.
10 problems · about 17 minutes · 6.EE.A.2, 6.EE.B.6
What this lesson teaches
The child writes an algebraic expression from a description in words.
- Name the unknown before you write anything.
- "Less than" and "divided by" reverse the order you hear them in.
- Brackets say that a whole sum is being multiplied, not just one part.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
3 problemsReview — Equivalent Expressions: 4(n + 3) expands to 4n + what?
Answer 12
Why 4n + 12.
Review — Letters for Numbers: If a = 8, what is 4a − 5?
Answer 27
Why 27.
Review — Exponents and Order of Operations: What is 5 + 2 × 3²?
Answer 23
Why 23.
Warm Up
Straightforward practice. Get the method working first.
3 problemsEvaluate 4n − 3 when n is 5.
Answer 17
Why 17.
Which is "four less than n"?
Answer n − 4
Why The four is taken from n.
Which is "double the sum of n and 5"?
Answer 2(n + 5)
Why The whole sum is doubled.
Build It Up
The same ideas with more to keep track of.
2 problemsEvaluate 3n + 2 when n is 5.
Answer 17
Why 15 then add 2.
Evaluate 2(n + 4) when n is 3.
Answer 14
Why Brackets first: 3 + 4.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Pencils: n pencils, and 4 more are bought. Evaluate the expression when n is 10.
Answer 14
Why 10 + 4 = 14.
The Boxes: Each box holds n pens, and there are 6 boxes. Evaluate when n is 8.
Answer 48
Why 6 × 8 = 48.