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The Problems
Are you spending time in the sun? If you are, you should know about protecting yourself from the sun's rays. Sunscreens help prevent the sun’s ultraviolet rays from reaching the skin and giving you a sunburn. Sunscreens are chemical agents that come in various strengths and are rated with a Sun Protection Factor (SPF). If your skin starts to turn red after 10 minutes in the sun, a sunscreen with an SPF 15 will theoretically prevent the reddening 15 times longer or 150 minutes. A sunscreen with an SPF 30 will theoretically prevent the reddening 30 times longer or 300 minutes. It seems that if the SPF is high enough you won’t sunburn. However, the effectiveness of the sunscreen should also be considered. No sunscreen can block 100% of the harmful ultraviolet rays (UVB) from the sun. An SPF 15 blocks 95% of the UVB rays and an SPF of 30 blocks 97% of the UVB rays. What percent more UVB rays are blocked when the protection is increased from SPF 15 to SPF 30? Express you answer to the nearest whole number?
Doug and Anna plan to kayak on the river near their home. The river flows at a rate of 4 miles per hour. In still water they paddle their kayaks at a constant rate of 6 miles per hour. They start and end their trip at the same place on the river. They kayak for exactly two hours, first going upstream and then downstream. What is the total length, in miles, of their trip on the river? Express your answer as a decimal to the nearest hundredth.
Paul and Mary inflate balloons with helium which are released to test the wind currents. Each spherical balloon is inflated at a constant rate. After 10 seconds the volume of the balloon is V cubic units. 10 seconds later the volume of the balloon is 2V cubic units. What percent greater is the radius of the balloon at 20 seconds than at 10 seconds? Express your answer to the nearest whole number.
