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------------------------------------------------ Select the correct answer.

A dust particle weighs [tex]$7.42 \times 10^{-10}$[/tex] kilograms. What is the weight of [tex]$5 \times 10^6$[/tex] dust particles represented in scientific notation?

A. [tex]3.71 \times 10^{-4}[/tex] kilograms
B. [tex]3.71 \times 10^{-3}[/tex] kilograms
C. [tex]37.1 \times 10^{-3}[/tex] kilograms
D. [tex]37.1 \times 10^{-4}[/tex] kilograms

Answer :

We start with the weight of one dust particle given as
[tex]$$
7.42 \times 10^{-10} \text{ kg}
$$[/tex]
and we have
[tex]$$
5 \times 10^{6}
$$[/tex]
dust particles.

To find the total weight, we multiply the weight of a single particle by the number of particles:

[tex]$$
\text{Total weight} = \left(7.42 \times 10^{-10}\right) \times \left(5 \times 10^{6}\right)
$$[/tex]

First, multiply the coefficients:

[tex]$$
7.42 \times 5 = 37.1
$$[/tex]

Next, add the exponents of the powers of 10:

[tex]$$
10^{-10} \times 10^{6} = 10^{-10+6} = 10^{-4}
$$[/tex]

Thus, the product becomes

[tex]$$
37.1 \times 10^{-4}.
$$[/tex]

To express this in proper scientific notation, we write the coefficient between 1 and 10. Notice that

[tex]$$
37.1 \times 10^{-4} = 3.71 \times 10^{-3},
$$[/tex]

since moving the decimal point one place to the left increases the exponent on 10 by 1.

Therefore, the weight of [tex]$5 \times 10^6$[/tex] dust particles is

[tex]$$
3.71 \times 10^{-3} \text{ kg}.
$$[/tex]

Comparing with the provided choices, the correct answer is:

[tex]$$
\boxed{3.71 \times 10^{-3} \text{ kilograms}}
$$[/tex].