Useless? Algebra is one of the few things I use regularly, almost daily. Anytime I solve for an unknown value, I am using algebra.
Here is a work example. A baby came in taking 2.5 mL of a 125 mg/5 mL solution of medication. Doing a little math, the dose in milligrams came to 62.5 mg, below the 10 mg/kg we wanted this 8.1 kg baby to receive. How much did we need to increase the dose? Oh, no! It's a classic "word problem" where we have to set up and solve for an unknown value!!!!
81 mg = 125 mg/5 mL x X mL
Multiply both sides by 5 mL gives us
5 mL x 81 mg = 125 mg x X mL
Now divide both sides by 125 mg...
3.24 mL = X
So I ended up prescibing 3.5 mL, both to make dosing more practical as well as to accommodate additional growth in the next year.
I get home at night and my husband wants a lemon drop martini. Making two for our extra-large martini glasses requires 1.5 cups of Absolut Citron; I only have 1.25 cups. How much do I need to cut the other ingredients?
1.25 cups = 1.5 cups x X
Dividing both sides by 1.5 cups...
0.83 = X
So I multiply the other ingredients by 0.83!
OK, I actually go to the liquor store...but you can see the practical use of the mathematics if this happened on Sunday (Oklahoma blue laws).
I have managed to live a full life with success in medicine and science without ever taking calculus, but I use algebra all the time. I will admit that I have not factored a polynomial since checking my kids' advanced algebra homework, but of all the math I learned, Algebra I has the most practical application. You may not realize it, but you use algebra as well.