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 : the order in which we carry out calculations.

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.