Question

Write an addition expression and a subtraction expression each with a value of 2.4 x 10^-3

Answer 1

Well,

You can just add up the numbers to get 2.4.

Example:
$1.0*10^{-3}+1.4*10^{-3}=10^{-3}(1.0+1.4)=2.4*10^{-3}$

In the same way you can make a subtraction problem.

Example:
$5*10^{-3}-2.6*10^{-3}=10^{-3}(5-2.6)=2.4*10^{-3}$