When you do not know a number yet, you can give it a letter.
Unknown is a number you have not worked out yet. A letter stands in for it.
Step 1: Let's Learn
Read it, or press Listen and follow the words.
An example
4 boxes of 6 pens, then 5 pens given away. Write it as 4 × 6 − 5 = p.
Two steps, in order
Work out the multiplication first, then the subtraction.
Check it is sensible
Roughly 24 take 5, so about 20. If you got 100, something went wrong.
A letter stands for the number you do not know yet
Instead of writing a box or a question mark, you can write a letter: 4 × n = 28. The n is a name for the missing number. It is not a mystery and it is not algebra to be afraid of — it is the same missing-number problem with tidier notation.
Two steps, two sentences
A bag holds 6 apples. Sam buys 4 bags and eats 3 apples. How many are left? First: 4 × 6 = 24. Then: 24 - 3 = 21. Write both lines. Using a letter, you might write n = 4 × 6 and then n - 3 for the answer.
Check the answer is reasonable
Estimate before calculating: 4 bags of about 6 is about 24, minus a few, so low twenties. An answer of 210 or 2 would be obviously wrong. With two steps there are twice as many places to slip, so the reasonableness check earns its keep.
Step 2: Try It Yourself
Tap and try it out.
4 × 6 = 24
4 rows of 6 makes 24.
Step 3: Watch an Example
One step at a time.
Watch Leo Use a Letter
4 boxes hold 6 pens each. 5 pens are given away.
- Step 1
He names the answer he wants: p, for pens left.
Step 4: Your Turn
Practice makes it stick.
The Bookshop
Problem 1 of 3
5 shelves hold 8 books each. 12 books are sold. How many are left?
books
The Party Bags
Problem 2 of 3
36 sweets are shared into 6 bags. Then 2 sweets are added to one bag.
sweets in that bag
The Coins
Problem 3 of 3
Ana has 3 bags of 9 marbles and loses 7. How many are left?
marbles
Two Steps Each
1 of 3
7 × 4 − 8 = ?
2 of 3
45 ÷ 5 + 6 = ?
3 of 3
6 × 6 − 10 = ?
Step 5: Quick Check
Show what you know.
Question 1 of 2
8 × 5 − 14 = ?
Question 2 of 2
What does a letter stand for in an equation?
What You Learned
- A letter stands for a number you have not found yet.
- Do the multiplication or division step first.
- Estimate to check the answer is sensible.