Scientists can determine the age of ancient objects by a method called radiocarbon dating. The bombardment of the upper atmosphere by cosmic rays converts bitrogen to a radioactive isotope of carbon, C-14, with a half life of about 5730 years. Vegetation absorbs carbon dioxide through the atmosphere and animal life assimilates C-14 through food chains. When a plant or animal dies it stops replacing its carbon and the amount of C-14 begins to decrease through radioactive decay. Therefore, the level of radioactivity must also exponentially decay. A parchment fragment was discovered that had about 74% as much C-14 radioactivity as does plant material on the earth today. Estimate the age of the parchment.

27

step-by-step explanation:

this may not be at all, but i use the same website you're using for school, and if i'm stuck doing one of these i try to look for it on the section.

d. $180

step-by-step explanation:

if the dimensions of the room is 9ft by 12 ft, we have the area of the floor as,

so the area of the floor is 108 square feet, converting that into square yards we get,

the cost of carpet is $15 per square yard, therefore the cost of carpet for 12 square yards is,

hence, the cost of carpet is $180.

assuming the dimensions of the room be,

15 ft by 12 ft

so, the area of the floor of that room is,

we can convert 180 square feet into square yards, we know that,

1 sq ft = 0.111 sq yard

so, 180 square feet is,

so the area of floor is 20 square yards.

now, the cost of carpet is 15 dollars per square yard, therefore the cost of carpet for 20 square yards is,

so, it will cost $300.

inch

step-by-step explanation:

yard and mile are too big.