The exponent is 6 while there are only 5 zeros because the exponent of a scientific notation does not depend on the number of zeros present. The exponent depends on the number of movements that the decimal point has moved. In this case, the decimal point is located on the right most zero of 3,500,000 it moved 6 numbers to the left to reach 3.5 so therefore 3.5 x 10^6