There are 100 centimeters in 1 meter. So to start with you must multiply 10000 by 100 to determine the number of centimeters in each race. This answer will be 1000000. Then to determine the number of centimeters in fifty races, you must multiply 1000000 by 50. This answer is 50000000. Then you must put it in scientific notation.
To do this you must move the decimal place over to the left until there is only one, nonzero number in front of it. Because you will move it to the left, your exponent will be positive. Therefore, your answer will be B.
