To Burn or not to Burn

TO BURN OR NOT TO BURN

Santa Claus and his elves have very sensitive skin. They're going on vacation in Florida and don't want to get sunburned. They are deciding what suntan lotion will protect them the best.

Now every suntan lotion has an SPF. The salesclerk tells Santa that an SPF of 2 blocks 50% of the UV rays, an SPF of 4 blocks 75% of the UV rays, and an SPF of 6 blocks 83(1/3)% of the UV rays.

Santa's doctor told him he must find an SPF that will block at least 90% of the UV rays. What is the smallest SPF Santa can use?

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What percent of the UV rays would be blocked with an SPF of 35?

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