Which is the best estimate for (6.3x10-19.9x10-) written in scientific notation? 6x10-4
60 x 10-5
6x 10?
60 x 10^6
is it C ?

Answer - B, 60x10^-5

We can see that 6.3 can be rounded to 6 and 9.9 can be rounded to 10. Therefore 6x10 gives you 60. However, when you are multiplying exponents, you have to add the exponents together. So 10^-2 x 10^-3 will give you 10^-5