Writing and Evaluating Expressions with Addition and Subtraction

Let $y$ represent the hours already committed by volunteers. The expression for the remaining hours needed is: $120 - y$.

Substitute $78$ for $y$ in the expression: $120 - 78$. This calculation results in 42 hours. Therefore, you still need volunteers for 42 more hours.

Let $ p $ represent the points earned in the first round, which are $15$. The points in the second round are double the first, so the expression for the total points is: $ p + 2p $.

Substitute 15 for $ p $ in the expression: $ 15 + 2 \times 15 $. Calculating this gives 45 points. Therefore, you have 45 points after two rounds.

Expression: $m - 4$, when $m = 20$, Solution: $16$

Expression: $p + 5$, when $p = 10$, Solution: $15$

Expression: $y - 12$, when $y = 50$, Solution: $38$

Expression: $s + 3 = 9$, solving for $s$ gives $s = 6$

An expression is a combination of numbers, variables, and operations that represents a particular value or set of values without an equality sign.

Writing expressions allows us to formulate complex real-world situations in mathematical terms, making them easier to analyse and solve.

Evaluating an expression involves performing the operations in the expression to find its numerical value.

In budgeting, if you start with a certain amount and spend some, you would write an expression like $ \text{starting amount} - \text{amount spent} $ to find out how much is left.

It helps in managing finances, planning events, and in any situation where keeping track of numbers is necessary.

Yes, using diagrams, tables, and algebraic notation can simplify the process. Tools like calculators and spreadsheet software can also assist in evaluating complex expressions.

Arithmetic expressions involve basic operations and numbers, while algebraic expressions also include variables representing unknown values.

Yes, errors can occur due to incorrect operation order or misunderstanding the problem, so careful calculation and review are important.

Yes, early exposure to these concepts builds a solid foundation for more advanced mathematical learning and problem-solving skills.

Common mistakes include incorrect use of operation symbols and misinterpreting the quantities involved in the problem. You should also make sure you use a different letter for each different variable.