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Day 5: Using a formula with changing or variable valuesDescription: Substituting values into a formula
Objective: The purpose of this exercise is to use variable or changing values in a formula to get several different answers (or outputs) based on different questions (or inputs).
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Mary starts 40 metres below ground and travels upwards at a speed of 6 metres per second for 15 seconds.

How far above ground is she at the end ?

Answer :  -40 + 6 × 15

=   -40 + 90

=   50 metres above ground.

Sometimes we want to try out the same question many different times but for different values of how long she was travelling for.

So. Question

Mary starts 40 metres below ground and travels upwards at a speed of 6 metres per second for 1, 2, 3, 5, 10, or 20 seconds.

How far above ground did she end up in each case.

For this question we write out our formula using a letter to represent that changing or variable value.

Formula:     -40 + 6 x n

So Ans1)   -40 + 6(1)

= -34

Ans2)   -40 + 6(2)

= -28

Ans3)   -40 + 6(3)

= -22

Ans4)   -40 + 6(5)

= -20

Ans5)   -40 + 6(10)

= +20

Ans6)   -40 + 6(20)

= +80

For each question we have the same formula    :   -40 + 6n    (which means -40 + 6 times by whatever value n is )

The letter n is called a variable  because it represents a variable value (In this case the length of time in seconds that Mary travelled for).