In algebra we will learn how to find the value of the variables by changing the subject in an equation or formula using the balance method.
To find the value of the variable using change of subject of formula and method of substitution:
The process of finding the value of algebraic expression by replacing the variables by the given value is called the method of substitution.
In this,
• Make the required variable as the subject.
• Substitute the values of all the variables except the subject.
• Now simplify and find the value of the subject.
WorkedOut Examples on Changing the Subject in an Equation or Formula
1. In the formula P = 2(l + b), find b when P = 36 cm and l = 10 m
Solution:
P = 2 (l + b)
P = 2l + 2b
P  2l = 2b
(P  2l)/2 = 2̶b/2̶
i.e., b = (P  2l)/2
b = (36  2 × 10)/2
b = (36  20)/2
b = 1̶6̶/2̶
b = 8
2. Given A = P {1 + (r/100)}ⁿ make r as the subject.
Given A = 1102.50 P = 1000 n = 2, find r.
Solution:
A = P {1 + (r/100)}ⁿ
A/P = {1 + (r/100)}ⁿ
= 100 {21/20  1}
= 100 {(21 – 20)/20}
= 1̶0̶0̶ × 1/2̶0̶
= 5
● Formula
Formula and Framing the Formula
Change the Subject of a Formula
Changing the Subject in an Equation or Formula
Practice Test on Framing the Formula
● Formula  Worksheets
Worksheet on Framing the Formula
Worksheet on Changing the Subject of a Formula
Worksheet on Changing the Subject in an Equation or Formula
7th Grade Math Problems
8th Grade Math Practice
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