The number of significant digits that an integer has is equal to the number of digits from its first nonzero digit to its last nonzero digit, inclusive. As seen below in boldface, this is a group of three digits:

205,000

Three is the correct response.

In a decimal expression, any leading zeroes of a decimal expression must be discounted as significant digits; all digits from the first nonzero digit onward must be counted. These digits are in boldface below:

0.03040

Four is the correct response.

To find the number of significant digits of a decimal expression with digits on both sides of the decimal point, count the digits from the first (nonzero) digit to the last digit. 60.000007 has eight digits, all of which are significant.

In a decimal expression, any leading zeroes of a decimal expression must be discounted as significant digits; all digits from the first nonzero digit onward must be counted. These digits are in boldface below:

0.080808080 

The figure has eight significant digits.

First, determine the number of significant digits in each factor. Since each factor includes only nonzero digits, the number of significant digits in each is simply equal to the number of digits. Thus, 7.21 and 2.713 have three and four significant figures, respectively.

Now, multiply the numbers outright. The product is 

The product must be rounded to the appropriate number of significant digits. This number must be the lesser of the numbers of significant digits that appear in the factors, which is three. Count from the first nonzero digit:

Rounded, this is 19.6, the correct response.

First, determine the number of significant digits in each factor. Each factor has one or more leading zeroes, and each has its final digit after the decimal point, so in each case, the number of significant digits is equal to the number of digits from the first nonzero digit to the last digit. 0.0456 and 0.53 have three and two significant digits, respectively.

Now, multiply the numbers outright. The product is 

The product must be rounded to the appropriate number of significant digits. This number must be the lesser of the numbers of significant digits that appears in the factors, which is two. Count from the first nonzero digit:

Rounded, this is 0.24, the correct response.

First, determine the number of significant digits in each factor. Both factors have leading zeroes, which must be discounted. Therefore, in each factor, the number of significant digits can be found by counting from the first nonzero digit to the final digit. 0.00421 and  0.00332 each have three significant digits.

Now, multiply the numbers outright. The product, ignoring any trailing zeroes, is 

The product must be rounded to the appropriate number of significant digits. This number must be the lesser of the numbers of significant digits that appears in the factors, which is three. Count from the first nonzero digit:

Rounded, this is 0.0000140, the correct choice. (Note that this trailing zero must be kept in order to have three significant digits.)

When adding numbers, accounting for significant digits, the sum must be rounded to the same place as the least precise of the numbers. 9.7000 and 4.81 have their final digits in the ten-thousandths and hundredths place, respectively; this makes 4.81 the less precise measurement, and the sum must be rounded to the nearest hundredth.

Now, add the numbers outright:

To the nearest hundredth, this is rounded down to 14.58, the correct response.

When subtracting numbers, accounting for significant digits, the difference must be rounded to the same place as the least precise of the numbers. 17.3 and 13.452 have their final digits in the tenths and thousandths place, respectively; this makes 17.3 the less precise measurement, and the difference must be rounded to the nearest tenth.

Now, subtract the numbers outright, and round to the nearest tenth.

To the nearest tenth, this is rounded down to 3.8, the correct response.

First, determine the number of significant digits in each factor. Both factors have leading zeroes, which must be discounted, and trailing zeroes after the decimal point, which must be counted; therefore, in each factor, the number of significant digits can be found by counting from the first nonzero digit to the final digit. 0.660 and 0.5550 have three and four significant digits, respectively. 

Now, multiply the numbers outright. The product, ignoring any trailing zeroes, is 

The product must be rounded to the appropriate number of significant digits. This number must be the lesser of the numbers of significant digits that appear in the factors, which is three. Count from the first nonzero digit:

Rounded, this is 0.366, the correct choice.