Answer:
The 90th percentile of the distribution is 6.512 ml.
Step-by-step explanation:
Normal Probability Distribution:
Problems of normal distributions can be solved using the z-score formula.
In a set with mean
and standard deviation
, the z-score of a measure X is given by:

The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the p-value, we get the probability that the value of the measure is greater than X.
Mean of 6 milliliters (ml) and a standard deviation of 0.4 ml.
This means that 
Find the dye amount that represents the 90th percentile (i.e. 90%) of the distribution.
This is X when Z has a p-value of 0.9, so X when Z = 1.28. Then




The 90th percentile of the distribution is 6.512 ml.