We want to multiply [tex]2.5\cdot10^{-10}[/tex] by [tex]7\cdot10^{-6}[/tex].
The numbers are written in scientific notation. So we expect the answer also to be in scientific notation.
the multiplication of the 10's, using the exponents rule is :
[tex]10^{-10}\cdot 10^{-6}=10^{-10+(-6)}=10^{-10-6}=10^{-16}[/tex]
the multiplication of the other 2 numbers is:
[tex]2.5\cdot7=17.5=1.75\cdot10[/tex]
(we write the number so that it has only one digit to the left of the decimal point).
Thus,
[tex](2.5\cdot10^{-10})\cdot(7\cdot10^{-6})=1.75\cdot10\cdot10^{-16}=1.75\cdot10^{-15}[/tex]
Answer: [tex]1.75\cdot10^{-15}[/tex]
