A paragraph could very well be one sentence, but it could just as easily be a long 20 sentence paragraph. It's usually thought of as being a complete separate thought and containing as many sentences are needed before you reach a natural breaking point to move on to the next paragraph. Hope that helped.
Centi-means one-hundredth, so 1metre = 100 centimeters, therefore 1 decameter = 10 x (100 centimeters) = 1000 centimeters. Hecto-means one hundred, therefore 1 hectometer = 100 meters = 10 decameters. Kilo-means one thousand, of course, so 1 kilometer = 1000 meters, and since 1 hectometer = 100 meters, 1 kilometer = 10 hectometers.
When converting measurements it is often helpful to use a little algebra. It is also important to memorize a couple of facts. Most people don't know how many kilometers (km) are in a meter (m), but they do know how many meters are in a kilmeter. There are 1000 m in 1 km. Therefore there is .001km in a meter or 10^-3 km in a meter.