Last updated on June 11th, 2025
The relationship between the two variables in mathematics is defined using proportions. It is of two types: direct or inverse proportion. Inverse proportion is when the value of one variable decreases and the other increases. Let’s explore more about this connection.
In mathematics, the two commonly used proportions are direct proportion and inverse proportion. Inverse proportion is the opposite of direct proportion.
Two values are in inverse proportion when one decreases as the other increases. If the product of the two quantities equals a constant value, regardless of the change in their values, they are considered to be in inverse proportion.
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The mathematical representation of the inversely proportional relationship of two quantities is given below:
x × y = k
y = k/x
x1 × y1 = x2 × y2
Direct and inverse proportionality are mathematical tools that measure the change in one quantity with the change in the other. The key differences between the two are listed below:
Direct Proportionality | Inverse Proportionality |
Two values increase or decrease proportionally. | If one quantity increases, the other decreases. |
Formula : y = kx | Formula: x y = k |
The graph gives a straight line. | The graph gives a curved line. |
For example: The more you buy the more you pay | For example: The more you eat, the less is on your plate. |
Learning about inversely proportional relationships helps children understand the mathematical connection between quantities. Let’s look at a few tips and tricks to understand this connection easily:
Inversely proportional relationships can be observed in many real-life situations. Understanding their real-world applications helps students apply the concept quickly. Let’s learn how it can be applied:
Learning inverse proportionality is easy once you understand what it is. However, students tend to make mistakes. Let’s look at a few common errors and the ways to avoid them
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If 2 students can complete a task in 10 days. How many days will it take if 5 students are assigned the same task?
It requires 4 days for 5 students to finish the task.
To find the number of days required to complete the task we use the formula,
x1 × y1 = x2 × y2
Here, x1 = 2
x2 = 5
y1 = 10
y2 = x1 × y1 / x2
y2 = 2 × 10 / 5
= 20 / 5 = 4
So, it requires 4 days for 5 students to finish the task.
A factory uses 6 machines to produce a batch of items in 9 hours. If 12 machines are used, how long will it take?
It will take 4.5 hours to produce the batch.
Here, we use the formula: k = x × y
k = 6 × 9 = 54
Now, we determine the value of y when x = 12
y = 54/12 = 4.5
So, using 12 machines, it will take 4.5 hours to produce the batch.
If 5 taps fill a water tank in 40 minutes, how long will it take if 8 taps are used?
It will take 25 minutes to fill a water tank with 8 taps.
Since, the number of taps ∝ 1/ time taken, we use the formula:
x1 × y1 = x2 × y2
5 × 40 = 8 × y
200 = 8y
Y = 200/8 = 25
So, it will require 25 minutes to fill a water tank with 8 taps.
A gas has a pressure of 150 kPa and a volume of 3 liters. If the pressure increases to 300 kPa, what will be the new volume?
The new volume is 1.5 liters.
Use the formula for inverse proportion:
x1 × y1 = x2 × y2
150 × 3 = 300 × y
450 = 300 y
y = 450/300 = 1.5
Therefore, the new volume is 1.5 liters.
A sound wave has a frequency of 400 Hz and a wavelength of 2 m. If the frequency is increased to 800 Hz, what will be the new wavelength?
The new wavelength is 1 meter.
We use the formula for inverse proportion as frequency and wavelength:
x1 × y1 = x2 × y2
400 × 2 = 800 × y
800 = 800y
y = 800/800 = 1
Therefore, the new wavelength is 1 meter.
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Dr. Sarita Tiwari is a passionate educator specializing in Commercial Math, Vedic Math, and Abacus, with a mission to make numbers magical for young learners. With 8+ years of teaching experience and a Ph.D. in Business Economics, she blends academic rigo
: She believes math is like music—once you understand the rhythm, everything just flows!