Question

(4.0 x 10^3)(2.8 x 10^-4)

Answer 1

Scientific nottaion is
(number that is less than 10 and more than or equalt to 1) times 10^x

so

remmeber
(a*b)(c*d)=(a)(b)(c)(d)=(a*c)(b*d)
so you can just move dem

also
(x^m)(x^n)=x^(m+n)

so

(4*10^3)(2.8*10^-4)=
group the exponent things together
(4*2.8)(10^3*10^-4)=
(11.2)(10^-1)=
don't forget that the first number has to be less than 10
11.2>10, so we have to factor out the 10
(1.12*10^1)(10^-1)=
(1.12)(10^1*10^-1)=
1.12*10^0

answer is 1.12*10^0
(first number has to be less than 10)

Answer 2

$(4.0 \times 10^3)(2.8 \times 10^{-4})\implies 4.0\times 2.8\times 10^3\times 10^{-4} \\ \quad \\ 11.2\times 10^{3-4}\impliedby \textit{same base, different exponent} \\ \quad \\ 11.2\times 10^{-1}$