When do you use algebra in real life?

Answer 1

An example:

Laser beams are sometimes modelled as being infinitely thin but in reality they do have some width and this width changes with respect to distance from the laser source. Using algebra it is possible to calculate the distance where the laser beam has a minimum width. This is useful because laser devices are used to read information on cd's and dvd's so minimizing the beam width at the cd/dvd will allow for more data to be stored on the cd/dvd.

Another example:

A fat man wants to take a boat ride. If he knows the dimensions of the boat then he can calculate the buoyant force on the boat and compare it to the gravitational force due to his mass. If the former is less than the latter, the boat will sink and he will get wet which will ruin his new pants (they dissolve in water)

Final example:

You have a cannon that shoots blocks of cheese and you want to shoot some smelly cheese through someone's bedroom window. You can use algebra to calculate the angle your cannon should make with the ground in order to hit your target and hence, give someone a smelly surprise.