Step by step
The question
Question: H = 2w + 15 is the height of a plant, in centimeters, after w weeks.
What does 2 mean?
We write the equation big, so we can label it.
1 What the letters mean
H is the height of a plant, in centimeters.
w is the number of weeks.
2 Make a small table
To see what each number does, we try a few weeks: 0, 1 and 2.
0 is where it starts.
w = 0: 2 times 0 is 0.
Plus 15 is 15.
w = 1: 2 times 1 is 2.
Plus 15 is 17.
w = 2: 2 times 2 is 4.
Plus 15 is 19.
Look at the values of H: 15, 17, 19.
Each time w goes up 1, H goes up by 2.
The same number every time.
3 Find the numbers in the table
Now we write the equation again, and label its numbers.
And 15?
At w = 0, 2 times 0 is 0.
Only 15 is left: the first number in the table.
So 15 is the height of a plant at 0 weeks: the start.
Where does plus 2 each time come from?
From 2w: 2 times w.
Each extra week adds one more 2.
Careful!
2 is multiplied by w, so each week adds another 2.
The start is the number alone.
4 Say it in words
So 2 means: the height of a plant goes up 2 centimeters for each extra week.
5 Check
Let's check with w = 3.
In words: start at 15, then add 2 three times.
We get 21.
The equation with w = 3: 2 times 3 is 6.
Plus 15 gives 21 too.
So the meaning is right!
Let's look back.
First: what the letters mean.
Then: make a small table.
Then: find the numbers in the table.
Then: say it in words.
Last: check.