# Changing the Subject in an Equation or Formula

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.

Worked-Out 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

(A/P)1/n = {1 + (r/100)}

(A/P)1/n - 1 = r/100

100 {(A/P)1/n - 1} = r

Therefore, 100 {(A/P)1/n - 1}

Substituting the values of A, P and n we get;

r = 100 {(1102.50/1000)1/2 - 1}

= 100 {(110250/1000)1/2 - 1}

= 100 {(441/400)1/2 - 1}

= 100 [{(21/20)2}1/2 - 1]

= 100 {(21/20)2 × 1/2 - 1}

= 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

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

Didn't find what you were looking for? Or want to know more information about Math Only Math. Use this Google Search to find what you need.

## Recent Articles

1. ### Worksheet on Word Problems on Fractions | Fraction Word Problems | Ans

Jul 16, 24 02:20 AM

In worksheet on word problems on fractions we will solve different types of word problems on multiplication of fractions, word problems on division of fractions etc... 1. How many one-fifths

2. ### Word Problems on Fraction | Math Fraction Word Problems |Fraction Math

Jul 16, 24 01:36 AM

In word problems on fraction we will solve different types of problems on multiplication of fractional numbers and division of fractional numbers.

3. ### Worksheet on Add and Subtract Fractions | Word Problems | Fractions

Jul 16, 24 12:17 AM

Recall the topic carefully and practice the questions given in the math worksheet on add and subtract fractions. The question mainly covers addition with the help of a fraction number line, subtractio…

4. ### Comparison of Like Fractions | Comparing Fractions | Like Fractions

Jul 15, 24 03:22 PM

Any two like fractions can be compared by comparing their numerators. The fraction with larger numerator is greater than the fraction with smaller numerator, for example $$\frac{7}{13}$$ > \(\frac{2…