Approximately what percentage of hydrogen peroxide by weight is in a 40-volume developer?
a.6%
b.3%
c.12%
d.9%
Explanation
Volume rating divided by roughly 3.3 gives the percent peroxide: 10 vol is about 3%, 20 vol about 6%, 30 vol about 9%, and 40 vol about 12%. 40 vol is reserved for high-lift permanent color and is not used for on-scalp bleach.
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