How to use solution of an inequality in the real world?

They seek to describe the way nature flows. Many of the simpler equations also describe financial concepts, like exponential growth. Exponential growth can describe the cultivation of microorganisms as well.

Addition and substraction is used in shopping.

Much of mathematics are also used in programming in order to make smart software.

You basically used equations everyday without even notice. Like when you have to calculate “How many dollars does the sum of your grocery stuffs equal to?”. Or a more complicated situation, if you need to be in the meeting at 9:30am, the travel distance is 10km and you can only leave after 8:30am, your driving speed should equal “x” km/h.”

Inequalities are used for comparison. “He is taller than me.” or “The iPhone with larger memory capacity is more expensive.”. A more complicated example is also with calculating your driving speed. “Now if there is expected traffic jam for 2km. You get out of the traffic jam at 9:00am, you have to drive faster than

“x” km/h to compensate for your loss time.”

Just some simple examples. There are a lots more out there, just look around.

by using injustices or by subtracting

i'm not sure i quite understand, could you provide more information?