acre-feet of water in 2.2 inches of rain over 43 sq km

[soccerball3211]

Hydraulic engineers in the United States often use, as a units of volume of water, the acre-foot, defined as the volume of water that will cover 1 acre (where 1 acre = 43560 ft2) of land to a depth of 1 ft. A severe thunderstorm dumped 2.2 in. of rain in 30 min on a town of area 43 km2. What volume of water, in acre-feet, fell on the town?

I keep getting 10625.53 acres and then I multiply by .183 feet to give me 1944.5 acre-feet. Does anyone know why my answer is coming out incorrectly?

 

[skeeter]

1 km² = 247.105381 acres

43(247.105381)(2.2/12) = 1948 acre-ft

close enough

 

[jsbeckton]

Always try to use the number in your calculators anwser to your first calculation in your second......and so on. It stores more digits than it shows and after 4 or 5 calculations, the rounding adds up as you have seen.

If you have a TI-89 it will give you fractions, thats best.

 

[soccerball3211]

Gold, which has a mass of 19.32 g for each cubic centimeter of volume, is the most ductile metal and can be pressed into a thin leaf or drawn out into a long fiber. (a) If a sample of gold with a mass of 7.000 oz, is pressed into a leaf of 6.000 μm thickness, what is the area (in m^2) of the leaf? (b) If, instead, the gold is drawn out into a cylindrical fiber of radius 2.200 μm, what is the length (in m) of the fiber?

For part A I calculated 1.712m^2
and for part B I calculated 675369 m
Part B doesn't seem right so could someone point me in the right direction?

Thank you