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Next, count the digits after the decimal point. There are $\text{three}$ digits after the decimal point. This number will be written as the exponent of $10.$ The power of $10$ is $4.$ It has a positive exponent. Therefore, the decimal point will be moved to the right $4$ times. In other words, the first factor $1.851$ will be multiplied by $10$ $\text{four}$ times. The diagram shows that the decimal point continues to move after the nonzero digits. Zeroes can be added to the end of the number until the move is done. Note that adding zeroes to the end of a decimal number after the decimal point does not change the value of the number. In this case, there are already three nonzero digits. Only one zero needs to be added to the end of the number. Now, the number is in standard form as a five-digit number.

Then, determine the power of $10.$ That is done by counting the number of digits before the new decimal point. There are $\text{six}$ digits before the decimal point. The given number $0.000002$ is less than $1.$ That means the exponent will be negative. Notice that the power of $10$ is negative. This means that the decimal point will be moved to the $\text{left six}$ times. A zero is added every time the decimal moves to the left of the given digits. Remember to write an additional zero before the decimal point. Finally, the number is rewritten in standard form as an eight-digit number.

	Population	Rounded
USA	$331002651$	$300000000$
Brazil	$212559417$	$200000000$
Turkey	$84339067$	$80000000$
China	$1439323776$	$1000000000$
Australia	$25499884$	$30000000$

Now all the rounded numbers can be rewritten as a single digit times a power of $10.$ Count the zeros to determine the power of $10$ for each number. For instance, the rounded population of the USA can be rewritten in this way. Apply the same method so the rounded populations of other countries in standard form can be rewritten in scientific notation.

	Population	Rounded	Scientific Notation
USA	$331002651$	$300000000$	$3\times 10^8$
Brazil	$212559417$	$200000000$	$2\times 10^8$
Turkey	$84339067$	$80000000$	$8\times 10^7$
China	$1439323776$	$1000000000$	$1\times 10^9$
Australia	$25499884$	$30000000$	$3\times 10^7$

Country	Population
USA	$3\times 10^8$
Brazil	$2\times 10^8$
Turkey	$8\times 10^7$
China	$1\times 10^9$
Australia	$3\times 10^7$

Examine the powers of $10.$ Begin with identifying the largest power. China has the largest. That means it has the greatest population. Now compare the numbers with the same power of $10.$ Start with $10^8$ because $10^8$ is greater than $10^7.$ The powers of $10$ for the US and Brazil are equal. That means their first factors should be compared. The value $3$ is larger than $2.$ That means the population of the USA is greater than Brazil. Next, compare the populations of Turkey and Australia. Again, the powers of $10$ are the same. This indicates that the values of $8$ and $3$ should be checked. Well, $8$ is greater than $3.$ That means the population of Turkey is greater than Australia. Now the countries can be sorted from greatest to least population.

1. The first factor must be greater than or equal to $1$ and less than $10.$
2. The second factor must be a power of $10.$

It is helpful to organize this check in the following way. Both numbers meet the two characteristics. They are written in scientific notation. Now their first factors can be multiplied by using the Commutative Property of Multiplication. Their second factors can be multiplied by using the Product of Powers Property. The product of the multiplication is already in scientific notation! Recall how to divide numbers written in scientific notation. The first factors are divided like fractions and the second factors are divided by using Quotient of Powers Property. Notice that the result is not in scientific notation yet because the first factor is less than $1.$ The decimal point needs to be moved one unit to the right. That move means the power of $10$ must be decreased by one. Now it is in scientific notation.

Begin by rewriting both numbers in scientific notation. Notice that $0.048$ is less than $1.$ The decimal point moves two units to the right to become greater than $1.$ Next, the two unit move to the right means the base $10$ power will have an exponent of $\text{-}2$. Now consider $24.$ A number greater than $10$ moves a certain number of units to the left. This case requires a one unit move to the left. Recall that movement to the left means the exponent of the base $10$ power will be positive. The second factor is $10^1.$ Now that both numbers are in scientific notation, multiply them by using Commutative Property of Multiplication and Product of Powers Property. The result is not in scientific notation. It will need to be rewritten. Follow the same method as done previously. Move the decimal point one unit to the left and increase the power of $10$ by that same value, $1.$ Finally, round the obtained result to two decimals. In a full day, the snail can move about $1.15\times 10^0$ or $1.15$ kilometers. Quite impressive! Now, rearrange the distance formula to use it for the time by dividing both sides of the equation by speed. Before using the obtained formula, rewrite the numbers to have them in scientific notation. To do so, move the decimal points to the right to make the first factors greater than or equal to $1$ and decrease the powers of $10$ according to amount of decimal points moved. Then, perform the division to find the time that the snail needs to move $1\times 10^{\text{-}3}$ kilometers. Since the first factor of the obtained result is less than $1,$ move the decimal point one unit to the right and decrease the power of $10$ one unit as well to have it in scientific notation. This means that the snail moves one meter in about $2.08\times 10^{\text{-}2}$ hours. For those curious, this is about $75$ seconds. Turns out snails are actually not that slow!

The powers of $10$ need to be the same to be able to add these numbers. The first number can be rewritten by moving the decimal point one unit to the right. That results in its power of $10$ decreasing by one unit. The first factors of the numbers can be added since these numbers are now like terms. Notice that the result is not in scientific notation because the first factor is greater than $10.$ It needs to be rewritten. The decimal point can be moved one unit to the left. That results in its power of $10$ increasing by one. In total, a typical large and small wind turbine produce $6.13\times 10^6$ kilowatt-hour energy per year. That is enough to meet the electricity demand of around $1600$ average households per year. Perform this operation by setting the powers of $10$ as the same. Recall that the first number was already rewritten in Part A. Subtraction can be performed now that they are like terms. The result is not in scientific notation. It can be rewritten by moving the decimal point one unit to the left. That results in the power of $10$ increasing by one unit. The difference in produced energies of the two type of wind turbines is $5.87\times 10^6$ kilowatt-hour per year.