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Question
Sunscreens block harmful ultraviolet (UV) rays produced by the sun. Each sunscreen has a Sun Protection Factor (SPF) that tells you how many minutes you can stay in the sun before you receive one minute of burning UV rays. For example, if you apply sunscreen with SPF 15, you get 1 minute of UV rays for every 15 minutes you stay in the sun.
A sunscreen with SPF 15 allows only `1/15` of the sun’s UV rays. What per cent of UV rays does the sunscreen abort?
Solution
A sunscreen with spf 15 allows only `1/15` of the sun's UV rays.
It means = `1 - 1/15 = 14/15` of the sun's UV rays abort by sunscreen.
In percentage = `(14/15)/1 xx 100`
= `1400/15`
= 93.333%
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