表の性別年代別利用者の構成比が分かるようにグラフ化した。次の図の性別年代別構成比グラフの Z に入る項目名として, 適切なものはどれか。
出典 平成21年度 春期 ITパスポート試験 問95
解説
問 95
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×Incorrectア
Women in their 30s account for 215 ÷ 1,582 = 13.6%, which rounds to 14% and does not become 19%. There are three sectors labeled 14% in the chart (men in their 40s 14.3%, women in their 50s 14.3%, women in their 30s 13.6%), and women in their 30s is the smallest of them, so among those three 14% sectors arranged in descending order it is the third (leftmost) one. That is a different position from the sector of Z (19%).
×Incorrectイ
Women in their 40s account for 348 ÷ 1,582 = 22.0%, the largest composition ratio among the 8 groups. It is already drawn in the chart as the “22%” sector placed first clockwise from the 12 o'clock position, immediately before Z. Therefore it is not the item that goes into Z, which is 19%.
×Incorrectウ
Men in their 40s account for 227 ÷ 1,582 = 14.3%, which rounds to 14% and does not match 19%. Furthermore, women in their 50s also number 227 (14.3%), so men in their 40s is merely one of the three sectors labeled 14% and cannot by itself occupy the 19% sector.
○エ
正解The composition ratio (percentage) is obtained as “the number of people in that group ÷ the total number of people overall × 100”. The total is the male subtotal 692 + the female subtotal 890 = 1,582 people. Calculating all 8 groups this way gives women in their 40s 22.0%, men in their 50s 18.6%, men in their 40s 14.3%, women in their 50s 14.3%, women in their 30s 13.6%, men in their 30s 7.2%, women in their 20s 6.3%, and men in their 20s 3.5%; rounded to integers, they are 22 / 19 / 14 / 14 / 14 / 7 / 6 / 4 (%). The labels of the pie chart run clockwise from the 12 o'clock position as 22% → Z(19%) → 14% → 14% → 14% → 7% → 6% → 4%, that is, in descending order of composition ratio. The only group that comes to 19% is “men in their 50s”, at 295 ÷ 1,582 = 18.6% ≒ 19%; moreover the sector of Z sits in the second position, right after the largest 22% (women in their 40s), and it corresponds exactly to men in their 50s, the group with the second-largest ratio. Therefore the item name that goes in Z is “men in their 50s” = エ.
ここがポイント
The denominator of a composition ratio (percentage) is the overall total. Here the denominator is 1,582 people, the male subtotal 692 plus the female subtotal 890; if the subtotal of only one gender is used as the denominator, every value goes wrong (for example, 295 ÷ 692 = 42.6%, which no longer corresponds to any choice).
A pie chart (composition ratio chart) usually arranges its sectors clockwise from the 12 o'clock position in descending order of composition ratio. By matching the sequence of labels written in the chart (22 → 19 → 14 → 14 → 14 → 7 → 6 → 4) against the descending order of the composition ratios you calculate yourself from the table, you can uniquely identify the hidden item. When several values are tied, using a value that appears only once (19% here) as the clue is the surest approach.