Answer
$4.21\times10^{-3}$
Work Step by Step
$0.00421$
Move the decimal point so that there is only one nonzero number to its left side. The number of times the decimal point is moved will be the magnitude of the exponent. If the decimal point is moved left, the exponent will be positive. If it is moved to the right, it will be negative.
$4.21\times10^{-3}$
