These are applications of the distributive property of multiplication over addition.
a(b+c) = ab + ac
It helps to be completely comfortable with that transformation (in both directions). It also helps to be completely comfortable with signed arithmetic (adding and subtracting, multiplying and dividing positive and negative numbers) and with identifying terms and their degree, variables, and coefficients.
Underlying all of this is a good grounding in counting and multiplying. Playing with quantities of physical objects, such as dominoes, cards, marbles, jacks, or Legos, can help. (A lot of kids don't do it that much anymore.) Cooking from recipes can help. (My favorite way to work with math in the kitchen is dividing the recipe for Monster Cookies.)
a(b+c) = ab + ac
It helps to be completely comfortable with that transformation (in both directions). It also helps to be completely comfortable with signed arithmetic (adding and subtracting, multiplying and dividing positive and negative numbers) and with identifying terms and their degree, variables, and coefficients.
Underlying all of this is a good grounding in counting and multiplying. Playing with quantities of physical objects, such as dominoes, cards, marbles, jacks, or Legos, can help. (A lot of kids don't do it that much anymore.) Cooking from recipes can help. (My favorite way to work with math in the kitchen is dividing the recipe for Monster Cookies.)
