Evaluate an expression/formula

We can find the value of an expression when given the values of x, y, etc.

Before we start, we will need to remind ourselves of BODMAS: the order in which we carry out calculations.

BODMAS = Brackets, Order, Division, Multiplication, Addition, Subtraction

Question

Find the value of 3x + 5y when x = 2 and y = -1.

To find the value of an expression, we need to substitute the given values for x and y into 3x + 5y.

3x + 5y

 = 3 \times 2 + 5 \times ( - 1)

Remember, BODMAS tells us to multiply before we add.

= 6 + ( - 5)

= 1

Question

Evaluate 5c - b + 2a when a = 3, b = 1 and c = 4.

5c - b + 2a

= 5 \times 4 - 1 + 2 \times 3

= 20 - 1 + 6

= 25

Question

An approximate formula which converts celsius temperatures to farenheit is F = 2C + 30.

Calculate F when C is 15.

F = 2C + 30

F = 2 \times 15 + 30

F = 30 + 30

F = 60

Therefore 15°C is approximately equal to 60°F.