I need help understanding this Algebra problem.

Hello ATS. So I'm having some trouble. Hoping someone can help me understand this logic because it is one of the only places I feel safe posting online.

So here's this problem:



Highlighted in red, I have an issue understanding HOW they achieved 1.20 to be used in the equation. The math checks out. It's all true, but I need to understand where did 1.20 come from and why is this the way to do it? For whatever reason, I can't compute this manually on paper. I'm doing something terribly wrong.

If you want to know what I'm doing this math for, it's because I suck at math and I'm looking to improve. Hoping to be guided in the right direction here. Any videos of the sort relating to this and help me understand better will help.

a reply to: Mizzijr

You are adding the 20% to 100% which equals 120% or multiplying by 1.20.

a reply to: AugustusMasonicus

Ok that makes sense and you made it extremely simple from a mathematics pov.

But, why do it this way? Why can't I just take 20% of 18 and subtract 3.60 from 18?

a reply to: Mizzijr

When you want to increase something by a percentage, you can express it as 1.x. So if you want to increase a number by 20% it is same as multiplying by 1.2. If you wanted to increase it by 30%, you'd multiply by 1.3, etc. Doubling the number you multiply by 2.

a reply to: Mizzijr

You can do it anyway it seems simpler to you and yields the correct awnser, I bet some fancy folk with free time could solve it with integrals...

Math is like that

originally posted by: Mizzijr
a reply to: AugustusMasonicus

Ok that makes sense and you made it extremely simple from a mathematics pov.

But, why do it this way? Why can't I just take 20% of 18 and subtract 3.60 from 18?

Because the base number is different. 20% of $18.00 is $3.60. 20% Of $15 = $3.00.

The question is telling you that the $18.00 is the result of increasing X by 20%. So X * 1.2 = $18. 1.2x = $18. 18 / 1.2 = $15.

originally posted by: Mizzijr
a reply to: AugustusMasonicus

Ok that makes sense and you made it extremely simple from a mathematics pov.

But, why do it this way? Why can't I just take 20% of 18 and subtract 3.60 from 18?

Because then 18-3.60=14.40, and then 3.60/14.40 would be 25%, not 20%

Another way to look at it is if 100% of the meal cost +20%, 120% is $18, 100% is...do the cross product

120....$18
100.... X

x=18*100/120 =$15

Thanks guys. Finally clicked for me. I hope the best for all of you. Wish me luck.

a reply to: Mizzijr

If you want an easier way to never fail math questions formulated like that make equations of everything

Total= price +%a +%b

%a=5/100*price, %b=15/100*price Total= price + price*5/100 + price*15/100

Total = price(1 + 5/100 + 15/100) Price= total/(1 + 5/100 + 15/100) price = 18/1.2

May seem fool to do this, but for someone dumb like me is the way to do it right

a reply to: Indigent

Well wtf?? Who would have known ATS could ever provide the "goodies"? I have an algebra test tomorrow and this thread has been monumentally helpful !!!!!-

I wish I had more critical thinking. Working on it tho:^)

Thanks Miz, and Indig!!!!!'

a reply to: Mizzijr

Anytime.

Cheers.