Step by step
The question
Question: 50 cells triple every day.
How many are there after 4 days?
1 Find the start and the factor
The start is 50.
Triple means times 3.
So the factor is 3.
start: a = 50
factor: b = 3
2 Write the rule
x is the number of days.
Each day we multiply by 3 again.
So y = 50 × 3ˣ.
y = 50 × 3x
Careful!
Tripling 4 times is times 3, 4 times over.
Not times 12.
Careful: not 50 × 3 × 4 = 600 ✗
3 Put in x = 4
After 4 days, x = 4.
y = 50 × 34
3 to the power 4 is 81.
34 = 81
So we multiply 50 by 81.
= 50 × 81
So it is 4050.
= 4050
4 Check
Let's check day by day.
We start at 50, and multiply by 3 each day.
After 4 days we get 4050 again.
It works!
after 4 days: 4050
Let's look back.
First: find the start and the factor.
Then: write the rule.
Then: put in x = 4.
Last: check.
Answer
= 4050