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平成26年度 秋期 ITパスポート試験 問93

This question's explanation and your answers so far.

問93
頻出度★☆☆

F 教育機関では,P,Q,R,S,T,U の六つの組がある。各組の受講生数は,P,Q 組が 35 名,R 組が 25 名,S,T,U 組が 30 名である。このたび,6 組共通のテストを行い,採点結果の分析を行うことになった。 〔テストの採点結果の分析の概要〕 (1) テストの問題数は 10 問で,1 問を 1 点として,10 点満点である。 (2) 図 1 は,テストの採点結果入力のワークシートである。ワークシートのセル B2~B36 には,P 組の受講生の得点を入力する。同様に,ワークシートの列 C~G に,それぞれ Q~U 組の得点を入力する。 (3) テストの採点結果の分析は,得点の平均(以下,平均点という)及び標準偏差を使って行う。 標準偏差は,得点のばらつきの度合いを表す指標である。受講生数がそれぞれ 100 人で,得点が 1~4 点に分布する表 1 の分布例 1~5 とその平均点及び標準偏差を例にとると,分布例 1 や分布例 2 のように,全員が同じ得点だった場合は,平均点に対して全く得点のばらつきがないことから標準偏差は 0 になる。また,分布例 3~5 のように,平均点が同じでも,得点のばらつきが大きいほど,標準偏差は大きくなる。 表 1 分布例 1~5 とその平均点及び標準偏差

得点分布例 1分布例 2分布例 3分布例 4分布例 5
10001020
21000504030
300504030
4010001020
平均点2.04.02.52.52.5
標準偏差0.0000.0000.5000.8061.025

図2のテストの採点結果入力のワークシートに,組別の得点分布表を作成するために,セルB40に計算式を入力してセルB40~G50に複写する。セルB40に入れる適切な式はどれか。 〔ワークシートの説明〕 (1) セルA40~A50には,得点を示す数値として,それぞれ0~10を入力する。 (2) セルB40~B50には,P組の0~10点の人数を,それぞれ表示する式を入力する。 (3) 同様にセルC40~C50にはQ組,セルD40~D50にはR組,セルE40~E50にはS組,セルF40~F50にはT組,セルG40~G50にはU組の得点別人数を表示する式を入力する。

ABCDEFG
1P組Q組R組S組T組U組
⋮
400
411
422
⋮⋮
5010

注記 網掛けの部分は,表示していない。 図2 テストの採点結果入力のワークシート

出典 平成26年度 秋期 ITパスポート試験 問93
解説

問 93

  • Incorrectア

    The range B$2 ~ B$36 is correct, but the condition is written as A$40, making the row absolute and the column relative. As a result, when the formula is copied downward the reference stays at A40 and never moves, so B41 through B50 also count «the number of students with 0 points», and the rows for 1 to 10 points all show the same value. Furthermore, when copied to the right only the column shifts, giving B$40, C$40, …, G$40, so the condition refers to cells of the distribution table itself instead of column A, where the scores are. The $ marks are placed the opposite way round (vertically vs. horizontally) from the correct answer.

  • イ

    正解 The correct answer is イ, COUNTIF(B$2 ~ B$36, = $A40). In spreadsheets, $ means «make that part an absolute reference (it does not move when the formula is copied)», while a part without $ is a relative reference and shifts automatically by the direction and distance of the copy. In this question, the formula entered in B40 is copied both to the right (column B → column G) and downward (row 40 → row 50), so for the range and for the condition you only need to ask «in which direction do I want it to shift?». The first argument, the range to be counted, is rows 2 to 36 of columns B to G, where each student's score for each class is stored. When copied to the right, the column should shift as class P (column B) → class Q (column C) → … → class U (column G), so the column is relative (it stays as B); when copied downward, the target must always stay in rows 2 to 36, so the rows are absolute ($2, $36) ⇒ B$2 ~ B$36. The score referred to by the second argument, the condition, is in rows 40 to 50 of column A. When copied downward, the row should shift as 0 points → 1 point → … → 10 points, so the row is relative (40); even when copied to the right, the score must always be read from column A, so the column is absolute ($A) ⇒ $A40. The formula is therefore COUNTIF(B$2 ~ B$36, = $A40). For example, copying this formula to D42 gives COUNTIF(D$2 ~ D$36, = $A42), which correctly counts how many students in class R (column D) scored 2 points.

  • Incorrectウ

    Both the range and the condition have their $ marks the wrong way round, so it is doubly wrong. In the range $B2 ~ $B36 the column is absolute, so even when copied to the right it keeps counting class P (column B); and because the rows are relative, copying downward gives $B3 ~ $B37, …, and at row 50 it becomes $B12 ~ $B46, so the target rows shift, pulling in row 37 and beyond (and even the area of the distribution table itself if copied far enough) and breaking the counting range. In the condition A$40 the row is also absolute, so every row can only count the number of students with 0 points, and copying to the right shifts the column so that it refers to cells of the distribution table itself.

  • Incorrectエ

    The condition $A40 is correct, but the $ marks in the range $B2 ~ $B36 are placed wrongly. Because the column is absolute, even when copied to column C and beyond it keeps counting the scores of class P (column B), so the columns for classes Q to U all show the same value as class P. In addition, because the rows are relative, copying downward shifts the counting range one row at a time to $B3 ~ $B37, …, and at row 50 to $B12 ~ $B46, so students in the upper rows are missed while row 37 and beyond (and even the area of the distribution table itself if copied far enough) get pulled in.

ここがポイント
  • Absolute vs. relative references: in a cell reference, the part marked with $ (the column letter or the row number) stays fixed when the formula is copied, while a part without $ shifts by the direction and distance of the copy. B$2 means «the column moves, the row does not», and $A40 means «the column does not move, the row does».
  • How to decide where the $ goes from the copy direction: for a formula that is copied both horizontally and vertically, judge each reference separately by asking «may the column shift when copied to the right?» and «may the row shift when copied downward?». Leave off the $ on the side you want to move, and put the $ only on the side you want to fix. COUNTIF (called 条件付個数 in the exam notation) is a function that returns the number of cells within the search range given as the first argument that satisfy the condition given as the second argument, and it is used to build frequency distribution tables.
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