Question

Please help *picture attached*

Answer 1

`\large\boxed{2.15\cdot10^(-3)}`

Explanation:

[ttex]\text{The scientific notation:}\ a\cdot10^k\\\\\text{where}\ 1\leq a<10,\ k\in\mathbb{Z}[/tex]

`\bold{METHOD\ 1:}\\\\10^(-3)=(1)/(10^3)=(1)/(1000)=0.001\qquad\text{used}\ a^(-n)=(1)/(a^n)\\\\2.8\cdot10^(-3)=2.8\cdot0.001=0.0028\\\\2.8\cdot10^(-3)-0.00065=0.0028-0.00065=0.00215\\\\0\underbrace{.002}_(3\to)15=2.15\cdot10^(-3)`

`\bold{METHOD\ 2:}\\\\2.8\cdot10^(-3)-0.00065=2.8\cdot10^(-3)-0.65\cdot10^(-3)\\\\=(2.8-0.65)\cdot10^(-3)=2.15\cdot10^(-3)`