Calculating the Speed

To find out which turtle has the fastest speed, we will calculate the speed of each turtle using the formula:

\[ \text{Speed} = \frac{\text{Distance}}{\text{Time}} \]

Let's calculate the speed for each turtle:

1. Bianca:

   • Distance = 21 centimeters
   • Time = 7 minutes \[ \text{Speed} = \frac{21 \text{ cm}}{7 \text{ min}} = 3 \text{ cm/min} \]

2. Michelle:

   • Distance = 24 centimeters
   • Time = 4 minutes \[ \text{Speed} = \frac{24 \text{ cm}}{4 \text{ min}} = 6 \text{ cm/min} \]

3. Sierra:

   • Distance = 18 centimeters
   • Time = 6 minutes \[ \text{Speed} = \frac{18 \text{ cm}}{6 \text{ min}} = 3 \text{ cm/min} \]

Now, summarizing the speeds:

• Bianca: 3 cm/min
• Michelle: 6 cm/min
• Sierra: 3 cm/min

From these calculations, Michelle is the fastest turtle.

The speed of the fastest turtle is 6 centimeters per minute.

So, the final answers are:

• Michelle is the fastest turtle.
• The speed of the fastest turtle is 6 centimeters per minute.