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 of the sun’s UV rays. What per cent of UV rays does the sunscreen abort?

Living on your own: Sanjay is looking for one-bedroom apartment on rent. At Neelgiri appartments, rent for the first two months is 20% off. The one bedroom rate at Neelgiri is Rs 6,000 per month. At Savana appartments, the first month is 50% off. The one bedroom rate at Savana appartments is Rs 7000 per month. Which apartment will be cheaper for the first two months? By how much?

For an amount, explain why, a 20% increase followed by a 20% decrease is less than the original amount.

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.

Suppose a sunscreen allows 25% of the sun’s UV rays.

a. What fraction of UV rays does this sunscreen block? Give your answer in lowest terms.

b. Use your answer from Part (a) to calculate this sunscreen’s SPF. Explain how you found your answer.

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 label on a sunscreen with SPF 30 claims that the sunscreen blocks about 97% of harmful UV rays. Assuming the SPF factor is accurate, is this claim true? Explain.