In algebra, a letter stands for a number. An expression like 3a + 2b is a calculation with letters. To evaluate it, substitute, which means swap each letter for its number.
If a = 7 and b = 5, then 3a + 2b = 3 × 7 + 2 × 5 = 21 + 10 = 31. Remember that 3a means 3 × a and ab means a × b. Use the order of operations: 4(a + b) means work out the bracket first, then multiply by 4.
Worked example
Find the value of 2ab when a = 9 and b = 7.
- 2ab means 2 × a × b.
- 2 × 9 × 7 = 126.
Answer:126
Key words
- variable
- a letter that stands for a number
- expression
- numbers and letters with operations
- substitute
- replace a letter with a number
Practise this
New questions every time.
Common Core-referenced: 6.EE.A.2c