Final answer:
The ratio 12cm to 18cm can be written as the fraction 2/3 in simplest form.
Step-by-step explanation:
To write the ratio 12cm to 18cm as a fraction in simplest form, you can divide both numbers by their greatest common divisor (GCD). The GCD of 12 and 18 is 6. So, dividing both numbers by 6 gives us the simplified fraction:
12cm to 18cm = 2cm to 3cm
Therefore, the ratio 12cm to 18cm can be written as the fraction 2/3 in simplest form.