Advertisements
Advertisements
प्रश्न
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.
- What fraction of UV rays does this sunscreen block? Give your answer in lowest terms.
- Use your answer from Part (a) to calculate this sunscreen’s SPF. Explain how you found your answer.
Advertisements
उत्तर
a. Sunscreen allows 25% of the sun’s UV rays.
∴ It blocks UV rays = 100 – 25 = 75%
= `75/100`
= `3/4`
b. Sunscreen allows 25% on `3/4` of UV rays.
It means, it protect = `1 - 3/4 = 1/4` of UV rays.
Hence, it’s a SPF 4.
APPEARS IN
संबंधित प्रश्न
On Sunday 845 people went to the Zoo. On Monday only 169 people went. What is the per cent decrease in the people visiting the zoo on Monday?
The population of a city decreased from 25,000 to 24,500. Find the percentage decrease.
Mohan's income is Rs 15500 per month. He saves 11% of his income. If his income increases by 10%, then he reduces his saving by 1%, how much does he save now?
In the year 2015 ticket to the world cup cricket match was ₹ 1,500. This year the price has been increased by 18%. What is the price of a ticket this year?
Increase of a number from 150 to 162 is equal to increase of ______ per cent.
15% increase in price of an article, which is Rs 1,620, is the increase of Rs ______.
Four times a number is a ______ % increase in the number.
In 2007 – 08, the number of students appeared for Class X examination was 1,05,332 and in 2008 – 09, the number was 1,16,054. If 88,151 students pass the examination in 2007 – 08 and 103804 students in 2008 – 09. What is the increase or decrease in pass % in Class X result?
In 1975, the consumption of water for human use was about 3850 cu.km/year. It increased to about 6000 cu.km/year in the year 2000. Find the per cent increase in the consumption of water from 1975 to 2000. Also, find the annual per cent increase in consumption (assuming water consumption increases uniformly).
