In algebra how do I figure out when to multiply add or subtract variables?

Sorry if I seem stupid but am a complete novice with it. Can someone please give me some very basic steps?In algebra how do I figure out when to multiply add or subtract variables?
Try to understand these principles.





Addition and Subtraction are firmly related to each other.


100 + 10 = 110


10 = 110 - 100





Multiplication and Division are related.


Divide 10 into 100 = Dividend 10


10 X 10 = 100


10, the Divisor X 10, the Dividend = 100.


If you are clear about those relationships, it will help you decide what method must be used.





It's a bit difficult without examples.


If you are trying to arrive at a Sum, this can be adding or subtraction.





If you're trying to arrive at a Result, this can be Multiplication or Division.





There are Compound calculations which combine those.


When that comes up, multiplication and/or division is done first, then, addition and/or subtraction.


It can be reversed, but it will be indicated with parentheses.





(2+3) X 4 = 5 X 4 Add then multiply, or divide if indicated.


(2X3) - 4 = 6 - 4 Multiply then subtract, or add as indicated.





Look at his.


I want to make a pound of M%26amp;Ms, with two colors. How many ounces of each do I need?


1/ 4 with black


3/4 with orange. (It's Halloween)





Can you see that you don't have the information to add or subtract?


You must first determine how many ounces of 1 pound, 16 oz, is needed of each fraction. So you must multiply first.


You can do these in your head, but you know the method.


1/4 X 16 = 4 oz.


3/4 X 16 oz = 12 oz.





Now, you can add the ounces = 16 oz, 1 pound.





You could do this with 4 colors, @ 1/4 pound each.





Another. If I make a basket.


1/4 pound of Walnuts


1/8 pound of Pistachio nuts


1/2 pound of Chestnuts


1/8 pound of Peanuts





How many pounds is in the basket.?


Can you see that you just add the fractions?





Now, how many ounces are in the basket?


Can you see that you must first calculate the number of ounces for each fraction? Then add the ounces. Then convert to pounds by division. Divide the ounces by 16 oz = pounds.





This is simple because they equal a pound, but this kind of calculation must be done, when a store mixes nuts or fruits for gift baskets.


Then they are able to calculate the price of the basket from the price per ounce for each kind and the fractions of a pound for each.





Obviously, they will charge extra for the time and the basket.





I hope this helps and isn't confusing.