A tape diagram showing the ratio of ice cream to milk as 3:4 means that for every 3 parts of ice cream, there are 4 parts of milk.
To find out how many parts of ice cream are needed for 10 parts of milk, we can set up a proportion based on the given ratio:
\[ \frac{\text{ice cream}}{\text{milk}} = \frac{3}{4} \]
Let \( x \) be the number of parts of ice cream needed for 10 parts of milk. We can set up the following equation:
\[ \frac{x}{10} = \frac{3}{4} \]
Now, we can cross-multiply to solve for \( x \):
\[ 4x = 3 \cdot 10 \] \[ 4x = 30 \] \[ x = \frac{30}{4} \] \[ x = 7.5 \]
So, there are 7.5 parts of ice cream needed for 10 parts of milk.