The value of an expression
Put numbers in place of the letters and it becomes a number.
What does it cost?
Ketaki’s cost is c × 35 + j × 60, where c is the number of coconuts and j is the kilograms of jaggery.
She buys more coconuts and the same jaggery. What happens to the cost?
What this lesson covers
The idea
An algebraic expression takes a number value when each letter-number in it is replaced by a number, and the value changes when those numbers change.
What does it cost?
Ketaki’s cost is c × 35 + j × 60, where *c* is the number of coconuts and *j* is the kilograms of jaggery.
She buys more coconuts and the same jaggery. What happens to the cost?
- It goes up
- It stays the same
- It goes down
Put numbers in
Set the number boxes. Each letter-number is replaced by its number, and the expression becomes a number.
A value for each choice of numbers
Replace each letter-number by a number and the expression works out to a number. Choose different numbers and the value changes.
An algebraic expression takes a number value when each letter-number in it is replaced by a number. When those numbers change, the value changes.
- c | j | c × 35 + j × 60 | value
- 10 | 5 | 10 × 35 + 5 × 60 | ₹650
- 2 | 1 | 2 × 35 + 1 × 60 | ₹130
- 1 | 3 | 1 × 35 + 3 × 60 | ₹215
Notes
An algebraic expression takes a number value when each letter-number is replaced by a number. Change the numbers and the value changes.
Check yourself
Find the value of c × 35 + j × 60 when *c* = 3 and *j* = 2.
Answer: 225 ₹
3 × 35 + 2 × 60 = 105 + 120 = 225.
Charu’s score is 7 × p − 3 × q. Find it when *p* = 5 and *q* = 2.
Answer: 29
7 × 5 − 3 × 2 = 35 − 6 = 29.
Charu’s score is 7 × p − 3 × q. The penalty *q* gets bigger and *p* stays the same. Her score…
The expression a + 3 has the value 26. What number was put in place of *a*?
Answer: 23
23 + 3 = 26, so *a* was 23.
- goes up. A bigger penalty takes away more.
- goes down — correct. Yes! 3 × q gets bigger, and it is taken away.
- stays the same. The value changes whenever a number in it changes.