※ Our check while writing this explanation could not fully confirm the published answer; scoring follows IPA's official key.
×Incorrectア
In Hokoku_100902 JohoTaro the numeric part has 6 digits. It is correct up to yymm＝1009, but the mistake is writing the following w as 02 in 2 digits. Rule ② of Table 1 states that “w is the serial number of the week within the month being reported, and the number of y, m, and w shows how many digits each takes”, and since the format contains only one w, the 2nd week must be written as the single digit 2. This is a typical wrong answer in which the 09 of the month leads you to zero-pad the week to 2 digits as well.
○イ
正解The correct answer is “イ Hokoku_10092 JohoTaro”. The file name format defined in Table 1 is “Hokoku_” ＋ yymm ＋ w ＋ author name, and you only need to apply the notation rules one item at a time. First, by notation rule ①, characters enclosed in “ ” are used in the file name just as they are, so it starts with Hokoku_. Next, by rule ②, yymm is the year and month being reported, the year uses the last 2 digits of the Western calendar year, and the number of y and m shows how many digits each takes; therefore September 2010 becomes yy＝10 and mm＝09, that is the 4 digits 1009. The biggest point is that the month is written as 09 with a leading zero, not as 9. Then, by the latter half of rule ②, w is the serial number of the week within each month, and since the format contains only one w it is 1 digit; because it is the 2nd week, w＝2. The author name is written as it is: JohoTaro. Finally, by rule ③, ＋ is a symbol that joins the characters before and after it and is not included in the file name, so joining everything gives Hokoku_10092JohoTaro, which matches choice イ. Note that the space that appears between the digits and the name in the choices is a typesetting gap in the original booklet; the format definition in Table 1 specifies no space, so by the rule they are joined together.
×Incorrectウ
In Hokoku_10902 JohoTaro the numeric part is 10902, a form in which, after the year 10, the month is written as the single digit 9 and the week as the 2 digits 02. By rule ② of Table 1 there are two m, so the month must be the 2 digits 09, and there is only one w, so the week is the single digit 2. Since only the position of the 0 is swapped compared with the correct 10092, it is hard to tell apart if you just glance at it without keeping the digit rule in mind. You should judge mechanically by the principle that the number of digits is decided by the number of characters in the format.
×Incorrectエ
In Hokoku_1092 JohoTaro the numeric part has only 4 digits. This is because the year 10, the month 9, and the week 2 were lined up with the month left as a single digit. By rule ② of Table 1 the month is expressed with the 2 digits of mm, so it should be 09, and the numeric part must be the total of 5 digits of yymm＋w (10092). It is also worth remembering that the purpose of keeping the number of digits in file names uniform is that sorting by name lines up years, months, and weeks in the correct order, and omitting the zero padding breaks that purpose.
ここがポイント
In the multi-part question format, the key to answering is to read accurately not only each individual question stem but also the naming rule given in the common description at the beginning (here, [Rules for creating business reports] Table 1), and to apply it exactly as it is.
In naming-rule notations such as yymm / w, the number of characters directly indicates the number of digits. A month that would come out as a single digit must be zero-padded to two digits, as in 09 (conversely, an item specified as one digit must not be zero-padded).
A string enclosed in quotation marks (Hokoku_) is used in the file name just as it is, while the ＋ symbol, which indicates concatenation, is not included in the actual file name.