The correct answer is (A) – 0.0015
The Decimal System enables writing numbers as large or as small as one wishes, using the decimal point.
Digits can be placed to the left or right of a decimal point, presenting values greater than one or less than one. To the left of the decimal point is a whole number (e.g. 45 in 45.589).
Moving to the left of the decimal point, every number gets 10 times bigger: ...Hundreds <- Tens <- Ones. To the right of the decimal point, the first digit means tenths (1/10). Moving to the right of the decimal point, every number gets 10 times smaller (one-tenth as big): Tenths -> Hundredths -> Thousandths…
As can be seen, all answer-options have 0 ones. Therefore, move to the right of the decimal point and compare their tenth values.
You can immediately dismiss answer-option (C) since it has 1 tenth while all other answer-options have 0 tenths. You are left with answer-options (A), (B), (D) and (E).
Comparing their hundredths values, you can immediately dismiss answer-option (B) since it has 1 hundredth while all other answer-options have 0 hundredths. You are left with answer-options (A), (D) and (E).
Therefore, move to the thousandths place and compare them:
Answer-option (A) – 0.0015 – 1 thousandths
Answer-option (D) – 0.0051 – 5 thousandths
Answer-option (E) – 0.00151 – 1 thousandths
As can be seen, you can dismiss answer-option (D) since it has the 5 thousandths, while (A) and (E) has smaller thousandths value of 1.
You are left with answer-options (A) and (E). Both have the same ten thousandths value of 5. However, while answer-option (A) ends there, answer-option (E) also have a hundred thousandths value of 1, making it larger than (A):
Answer-option (A) – 0.0015 – 0 hundred thousandths
Answer-option (E) – 0.00151 – 1 hundred thousandths
Therefore, answer-option (A) presents the smallest value.
Notice! Moving further to the right, the absence of digits is equivalent to writing 0. For example:
Answer-option (A) - 0.0015 can also be written as 0.00150, making it easier to compare with answer-option (E):
Answer-option (A) – 0.00150
Answer-option (E) – 0.00151
Notice! In case all or some of the answer-options have the same tenths/hundredths/thousandths values etc. move on to the next place to the right of the decimal point and compare the values, until you find a difference.