To find out what percentage Vinh has saved towards the standing mixer, you can use the formula:
\[ \text{Percentage Saved} = \left( \frac{\text{Amount Saved}}{\text{Total Cost}} \right) \times 100 \]
In this case, Vinh has saved $160 and the total cost of the mixer is $400.
\[ \text{Percentage Saved} = \left( \frac{160}{400} \right) \times 100 \]
Calculating this gives:
\[ \text{Percentage Saved} = 0.4 \times 100 = 40% \]
Therefore, Vinh has saved 40% of the cost of the standing mixer.