It is more effective if I explain using examples. So, for multiplication, you just have to multiply the magnitude, then add the exponents of the base 10. For example, when you multiply 5.2×10³ and 1.6×10², the solution would be:
(5.2)(1.6)(10³⁺²) = 8.32×10⁵
Now, for division, you will have to divide the magnitudes, and subtract the exponents by numerator minus denominator. The solution is as follows:
(5.2/1.6)(10³⁻²) = 3.25×10¹