1. What is Substitution in Algebra?
Substitution means replacing. In algebra, when we replace a variable with a number, we call it substitution.
For example, consider the expression 2x + 3.
Let us assume x = 2. So to substitute x, replace it with 2. When we do this replacement, we can write 2 × 2 + 3.
Note when we substitute a variable, we must always follow the order of operations (BIDMAS or BODMAS) rule to calculate the value after substitution.
Hence, 2 × 2 + 3 = 4 + 3 = 7.
1.1 Example Questions on Substitution
Example 1: If a = 2, b = -1 and c = 1 find 2a - 4b + 5c²
Solution : Substituting a, b and c with their values we get,
2a - 4b + 5c² = 2 × 2 - 4 × (-1) + 5 × 1²
Following BIDMAS rule,
= 2 × 2 - 4 × (-1) + 5 × 1 (first calculate Indices)
= 4 + 4 + 5 (then multiplication)
= 13 (then addition)
Example 2: Equation to convert fahrenheit (F) to Celsius (C) is given by:
F = 9⁄5 × C + 32
Work out the temperature in Fahrenheit if C = 35.
Solution: Substituting C = 35 in the equation we get,
F = 9⁄5 × 35 + 32
Following BIDMAS rule,
F = 9 × 7 + 32 (First division)
F = 63 + 32 (then multiplication)
F = 95 (then addition)
