Variables & Expressions
Sunny starts where the letters come from: what x is actually standing in for, and why 3x is one thing and not two.
Captions on every lesson. Nothing to sign up for.
The lesson runs on YouTube. Everything you need afterwards is on this page.
What this lesson settles
What a letter stands for
A variable holds a number you do not know yet. It is a placeholder, not a mystery.
Expression or equation
An expression is something to read. An equation makes a claim, and a claim can be balanced.
How to read 3x out loud
“Three times x.” The multiplication sign is invisible, which is exactly what trips people up.
Bandit adds what cannot be added
Bandit added the 3 and the 7 like they were the same kind of thing. Can you catch it in five seconds?
He guesses out loud every day so you never have to be the one who is wrong.
Bandit wrote
Sunny’s fix
3x counts x’s. 7 counts ones. Different things do not combine.
One step at a time
Evaluate 3x + 7 when x = 4. Same colours as the videos: blue is the variable, white is what you were given, orange is work in progress, green is final.
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3x + 7, x = 4
What you were given.
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3(4) + 7
Substitute. The 4 takes the place of x — the operation does not change.
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12 + 7
Multiply before you add.
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19
Final. Correct.
Step 1 of 4
Write it before you scroll
How do you write seven more than a number n as an expression?
seven more than n = ?
If you got it, good. If you did not, you are exactly where the lesson expects you to be. Watch the substitution part again and come back.
One day’s practice, printed and done
Twelve questions on today’s lesson, the worked answers behind them, and a Final Unlock at the end for anyone who wants the hard one.
- Free, and no account to make
- Worked answers included, not just a key
- Prints clean in black and white
- Friday’s Boss Prep is in the same pack
- Monday’s Mission Debrief video walks the answers next week.
Words from this lesson
The rest of Week 1
Five lessons, five Missions, one Boss Battle on Friday.
Beat Friday’s Boss Battle for a shot at Monday’s Elite wall — Solver Squad Elite.