Example: A pen costs x złoty and a notebook costs 1 złoty more than the pen. The expression 4(x+1) + 3x represents the cost of 4 notebooks and 3 pens.

Definition: An algebraic expression is a combination of variables, numbers, and mathematical operations that represent a value or quantity.

Highlight: When solving age-related problems, it's crucial to account for the time progression correctly, as shown in the problem where both Krzyś and his father age by 6 years.

Example: For the expression 10-3y, when y=2, we substitute and calculate: 10-3(2) = 10-6 = 4

Vocabulary: Like terms are terms that have the same variables raised to the same powers.

Definition: Combining like terms means adding or subtracting terms with the same variables and exponents.

Example: When a number k is increased 15 times to get 40, we write the equation k·15 = 40

Highlight: In percentage problems, it's essential to understand that a 10% reduction means working with 90% of the original amount.

Definition: A solution to an equation is a value that makes the equation true when substituted for the variable.