seientific notation

a) 2.50000 * 0.0000004=?
2.5 * 4 *10^(-7)
10 *10^(-7)
1 * 10^(-6)

b) (3.2*10^5)*(6.25*10^2) =?
(3.2*6.25)* (10^5)*(*10^2)
(20) * (10^7)
(2.0 *10^1) * (10^7)
2.0 * 10^8

c) (1.2*10^ -4)*(8.5*10^ -20)=?
(1.2 * 8.5)*( 10^ -4) * (10^ -20)
10.2 * 10^(-24)
1.02 * 10^1 * 10^(-24)
1.02 * 10^(-23)

d) (4*10^21)*(2.5*10^10)=?
(4*2.5)* (10^21 * 10^10)
10* (10^31)
1.0 * 10^32

e) 9.45*10^9
----------- ------- = ?
3.15*10^5

= (9.45/3.15) * 10^4
= 3.00 * 10^4

f) 7.47*10^12
------------------ = ?
6.14*10^-5

= (7.47/6.14) * 10^17
= 1.217 * 10^17