Algebra

For grown-ups: this lesson in words

Year 6 · Maths

Algebra: I can use letters to stand for numbers in formulae, sequences and missing number problems.

1. At a party, each child gets 2 balloons. Here are Sam's 2 balloons.

   Mei gets 2 balloons, and Kofi gets 2 balloons. That is 3 children.

   Join them all: 2 + 2 + 2 = 6 balloons, or 2 × 3 = 6.

   A rule with letters: b = 2 × c. b is the number of balloons, c is the number of children.

   Picture: Sam: 2 balloons, Mei: 2 balloons and Kofi: 2 balloons. The groups are pushed together and counted. 6 balloons altogether.

2. Now c = 5: 5 children. Here are 5 rows of 2 balloons, one row for each child.

   Count in 2s: 2, 4, 6, 8, 10.

   b = 2 × c, so b = 2 × 5 = 10.

   Putting 5 in place of c is called substituting. A rule like this is a formula.

   Picture: An array of 5 rows of 2 balloons. The rows are counted in 2s: 2, 4, 6, 8 and 10.

3. Your turn: Here is a formula: w = 2 × b. w is the number of wheels, b is the number of bikes. Here are 4 bikes, so b = 4. What is w?

   Picture: An array of 1 row of 4 bikes.

   Choose one:

   • 6
   • 8
   • 24

   Answer

   The answer: 8

   w = 2 × 4 = 8. The 4 bikes have 8 wheels.

   Picture: 4 rows of 2 counters, one row for the 2 wheels of each bike, counted in 2s: 2, 4, 6, 8.

Words to know

formula:

A rule written with letters and numbers, like w = 2 × b.

substitute:

Put a number in place of a letter.

sequence:

A list of numbers that follow a rule, like 2, 5, 8, 11.

term:

One number in a sequence.

unknown:

A number we do not know yet. We give it a letter.