□に当てはまる数を答えなさい。
- ヒント
- 【 分数の逆算 】
・帯分数は仮分数になおす。
・「 等式の両辺に同じ数をかけて（ 割って ）も等式は成り立つ 」ことを利用して、整数になおせる場合はなおす。
a = b
a × c = b × c
a ÷ c = b ÷ c
【 小数の逆算 】
・基本的に小数は分数になおす。（ 例外あり ）
【 分数・小数混合の逆算 】
・基本的に小数は分数になおす。（ 例外あり ）
問１
\(7\displaystyle\frac{1}{7}\) × ( \(\displaystyle\frac{1}{8}\) + □ ｰ \(\displaystyle\frac{1}{20}\) ) + \(\displaystyle\frac{1}{28}\) = \(1\displaystyle\frac{2}{7}\)
- 答え
- \(\displaystyle\frac{1}{10}\)
- 解き方
- \(7\displaystyle\frac{1}{7}\) × ( \(\displaystyle\frac{1}{8}\) + □ – \(\displaystyle\frac{1}{20}\) ) + \(\displaystyle\frac{1}{28}\) = \(1\displaystyle\frac{2}{7}\)
\(\dfrac{50}{7}\) × ( \(\dfrac{1}{8}\) + □ – \(\dfrac{1}{20}\) ) = \(\dfrac{9}{7}\) – \(\dfrac{1}{28}\) = \(\dfrac{36\ -\ 1}{28}\) = \(\dfrac{35}{28}\) = \(\dfrac{5}{4}\)
\(\dfrac{1}{8}\) + □ – \(\dfrac{1}{20}\) = \(\dfrac{\cancelto{1}{5}}{4}\) × \(\dfrac{7}{\cancelto{10}{50}}\) = \(\dfrac{7}{40}\)
□ = \(\dfrac{7}{40}\) + \(\dfrac{1}{20}\) – \(\dfrac{1}{8}\)
□ = \(\dfrac{7\ +\ 2\ -\ 5}{40}\) = \(\dfrac{4}{40}\) = \(\dfrac{1}{10}\)
問２
{ □ – \(\dfrac{4}{5}\) ÷ ( \(\dfrac{5}{6}\) – \(\dfrac{1}{2}\) ) } × 4 = 16
- 答え
- \(6\dfrac{2}{5}\)（ または 6.4 ）
- 解き方
- { □ – \(\dfrac{4}{5}\) ÷ ( \(\dfrac{5}{6}\) – \(\dfrac{1}{2}\) ) } × 4 = 16
{ □ – \(\dfrac{4}{5}\) ÷ ( \(\dfrac{5}{6}\) – \(\dfrac{3}{6}\) ) } = 16 ÷ 4
□ – \(\dfrac{4}{5}\) ÷ \(\dfrac{\cancelto{1}{2}}{\cancelto{3}{6}}\) = 4
□ – \(\dfrac{4}{5}\) × 3 = 4
□ – \(\dfrac{12}{5}\) = 4
□ = 4 + \(\dfrac{12}{5}\) = \(\dfrac{32}{5}\) = \(6\dfrac{2}{5}\)
問３
4.368 ÷ □ – 1.26 ÷ 14 = 1.002
- 答え
- 4
- 解き方
- 4.368 ÷ □ – 1.26 ÷ 14 = 1.002
4.368 ÷ □ – 0.09 = 1.002
4.368 ÷ □ = 1.002 + 0.09 = 1.092
1.092 × □ = 4.368
□ = 4.368 ÷ 1.092 = 4
問４
3 + ( □ + \(1\dfrac{1}{4}\) ) × 2.5 = 18
- 答え
- \(4\dfrac{3}{4}\)（ または 4.75 ）
- 解き方
- 3 + ( □ + \(1\dfrac{1}{4}\) ) × 2.5 = 18
( □ + \(\dfrac{5}{4}\) ) × \(\dfrac{5}{2}\) = 18 – 3 = 15
□ + \(\dfrac{5}{4}\) = \(\cancelto{3}{15}\) × \(\dfrac{2}{\cancel{5}}\) = 6
□ = 6 – \(\dfrac{5}{4}\) = \(\dfrac{24\ -\ 5}{4}\) = \(\dfrac{19}{4}\) = \(4\dfrac{3}{4}\)
問５
\(2\dfrac{6}{7}\) – \(\dfrac{1}{7}\) × ( □ – 4.5 ) = \(2\dfrac{1}{2}\)
- 答え
- 7
- 解き方
- \(2\dfrac{6}{7}\) – \(\dfrac{1}{7}\) × ( □ – 4.5 ) = \(2\dfrac{1}{2}\)
\(\dfrac{1}{7}\) × ( □ – 4.5 ) = \(2\dfrac{6}{7}\) – \(2\dfrac{1}{2}\)
□ – 4.5 = ( \(\dfrac{20}{7}\) – \(\dfrac{5}{2}\) ) × 7 = 20 – 17.5 = 2.5
□ = 2.5 + 4.5 = 7
問６
1 – □ × ( 0.8 – \(\dfrac{1}{2}\) ) = \(\dfrac{3}{5}\)
- 答え
- \(1\dfrac{1}{3}\)
- 解き方
- 1 – □ × ( 0.8 – \(\dfrac{1}{2}\) ) = \(\dfrac{3}{5}\)
1 – □ × ( 0.8 – 0.5 ) = 0.6
□ × 0.3 = 1 – 0.6 = 0.4
両辺を 10 倍する
□ × 3 = 4
□ = 4 ÷ 3 = \(\dfrac{4}{3}\) = \(1\dfrac{1}{3}\)
問７
3 – ( 7.5 × \(\dfrac{2}{21}\) – 0.8 ÷ □ ) = \(2\dfrac{6}{7}\)
- 答え
- \(1\dfrac{2}{5}\)
- 解き方
- 3 – ( 7.5 × \(\dfrac{2}{21}\) – 0.8 ÷ □ ) = \(2\dfrac{6}{7}\)
3 – ( \(\dfrac{\cancelto{5}{15}}{\cancel{2}}\) × \(\dfrac{\cancel{2}}{\cancelto{7}{21}}\) – \(\dfrac{4}{5}\) ÷ □ ) = \(\dfrac{20}{7}\)
\(\dfrac{5}{7}\) – \(\dfrac{4}{5}\) ÷ □ = 3 – \(\dfrac{20}{7}\) = \(\dfrac{21\ -\ 20}{7}\) = \(\dfrac{1}{7}\)
\(\dfrac{4}{5}\) ÷ □ = \(\dfrac{5}{7}\) – \(\dfrac{1}{7}\) = \(\dfrac{4}{7}\)
\(\dfrac{4}{7}\) × □ = \(\dfrac{4}{5}\)
□ = \(\dfrac{4}{5}\) × \(\dfrac{7}{4}\) = \(\dfrac{7}{5}\) = \(1\dfrac{2}{5}\)
問８
( □ – \(\dfrac{5}{12}\) ) × \(1\dfrac{1}{8}\) = \(1\dfrac{11}{16}\)
- 答え
- \(1\dfrac{11}{12}\)
- 解き方
- ( □ – \(\dfrac{5}{12}\) ) × \(1\dfrac{1}{8}\) = \(1\dfrac{11}{16}\)
( □ – \(\dfrac{5}{12}\) ) × \(\dfrac{9}{8}\) = \(\dfrac{27}{16}\)
□ – \(\dfrac{5}{12}\) = \(\dfrac{\cancelto{3}{27}}{\cancelto{2}{16}}\) × \(\dfrac{\cancelto{1}{8}}{\cancelto{1}{9}}\) = \(\dfrac{3}{2}\)
□ = \(\dfrac{3}{2}\) + \(\dfrac{5}{12}\) = \(\dfrac{18\ +\ 5}{12}\) = \(\dfrac{23}{12}\) = \(1\dfrac{11}{12}\)
問９
7 × 13 + □ × 6 + \(4\dfrac{1}{2}\) = 100
- 答え
- \(\dfrac{3}{4}\) ( または 0.75 )
- 解き方
- 7 × 13 + □ × 6 + \(4\dfrac{1}{2}\) = 100
91 + □ × 6 + 4.5 = 100
□ × 6 = 100 – 91 – 4.5 = 4.5
□ = \(\dfrac{4.5}{6}\) = \(\dfrac{45}{60}\) = \(\dfrac{3}{4}\)
問１０
7 – ( □ – 1.4 ÷ \(2\dfrac{4}{5}\) ) × 5 = 1
- 答え
- \(1\dfrac{7}{10}\) ( または 1.7 )
- 解き方
- 7 – ( □ – 1.4 ÷ \(2\dfrac{4}{5}\) ) × 5 = 1
7 – ( □ – \(\dfrac{7}{5}\) ÷ \(\dfrac{14}{5}\) ) × 5 = 1
( □ – \(\dfrac{\cancelto{1}{7}}{\cancelto{1}{5}}\) × \(\dfrac{\cancelto{1}{5}}{\cancelto{2}{14}}\) ) × 5 = 7 – 1 = 6
□ – \(\dfrac{1}{2}\) = 6 ÷ 5 = \(\dfrac{6}{5}\)
□ = \(\dfrac{6}{5}\) + \(\dfrac{1}{2}\) = \(\dfrac{12\ +\ 5}{10}\) = \(\dfrac{17}{10}\) = \(1\dfrac{7}{10}\)
問１１
( \(1\dfrac{6}{7}\) × \(1\dfrac{1}{6}\) – \(\dfrac{2}{7}\) ) ÷ \(\dfrac{1}{3}\) = □ × \(\dfrac{1}{2}\) + 4 ÷ 3.5
- 答え
- 9
- 解き方
- ( \(1\dfrac{6}{7}\) × \(1\dfrac{1}{6}\) – \(\dfrac{2}{7}\) ) ÷ \(\dfrac{1}{3}\) = □ × \(\dfrac{1}{2}\) + 4 ÷ 3.5
( \(\dfrac{13}{7}\) × \(\dfrac{7}{6}\) – \(\dfrac{2}{7}\) ) × 3 = □ × \(\dfrac{1}{2}\) + 4 ÷ \(\dfrac{7}{2}\)
( \(\dfrac{13}{6}\) – \(\dfrac{2}{7}\) ) × 3 = □ × \(\dfrac{1}{2}\) + 4 × \(\dfrac{2}{7}\)
\(\dfrac{13}{2}\) – \(\dfrac{6}{7}\) = □ × \(\dfrac{1}{2}\) + \(\dfrac{8}{7}\)□ × \(\dfrac{1}{2}\) = \(\dfrac{13}{2}\) – \(\dfrac{6}{7}\) – \(\dfrac{8}{7}\) = \(\dfrac{91\ -\ 12\ -\ 16}{14}\) = \(\dfrac{63}{14}\) = \(\dfrac{9}{2}\)
□ = \(\dfrac{9}{2}\) × 2 = 9
問１２
5.21 × □ = 0.521 × 62
- 答え
- 6.2
- 解き方
- 5.21 × □ = 0.521 × 62
5.21 × □ = 0.521 × 62
両辺を 0.521 で割る
10 × □ = 62
□ = 62 ÷ 10 = 6.2
問１３
( \(\dfrac{1}{2}\) – □ ) ÷ 0.4 × \(1\dfrac{1}{3}\) = 1
- 答え
- 0.2（ または \(\dfrac{1}{5}\) ）
- 解き方
- ( \(\dfrac{1}{2}\) – □ ) ÷ 0.4 × \(1\dfrac{1}{3}\) = 1
( \(\dfrac{1}{2}\) – □ ) ÷ \(\dfrac{2}{5}\) × \(\dfrac{4}{3}\) = 1
( \(\dfrac{1}{2}\) – □ ) × \(\dfrac{5}{\cancel{2}}\) × \(\dfrac{\cancelto{2}{4}}{3}\) = 1
( \(\dfrac{1}{2}\) – □ ) × \(\dfrac{10}{3}\) = 1
\(\dfrac{1}{2}\) – □ = 1 × \(\dfrac{3}{10}\)
□ = \(\dfrac{1}{2}\) – \(\dfrac{3}{10}\) = 0.5 – 0.3 = 0.2
問１４
2 ÷ ( □ ÷ \(1\dfrac{1}{4}\) – 3.52 ÷ 0.8 × \(\dfrac{1}{4}\) ) = \(\dfrac{1}{2}\)
- 答え
- \(6\dfrac{3}{8}\) ( または 6.375 )
- 解き方
- 2 ÷ ( □ ÷ \(1\dfrac{1}{4}\) – 3.52 ÷ 0.8 × \(\dfrac{1}{4}\) ) = \(\dfrac{1}{2}\)
2 ÷ ( □ ÷ \(\dfrac{5}{4}\) – 4.4 × \(\dfrac{1}{4}\) ) = \(\dfrac{1}{2}\)
2 ÷ ( □ × \(\dfrac{4}{5}\) – 1.1 ) = \(\dfrac{1}{2}\)
\(\dfrac{1}{2}\) × ( □ × \(\dfrac{4}{5}\) – 1.1 ) = 2
□ × \(\dfrac{4}{5}\) – 1.1 = 2 × 2 = 4
□ × \(\dfrac{4}{5}\) = 4 + 1.1 = 5.1
□ = \(\dfrac{51}{10}\) × \(\dfrac{5}{4}\) = \(\dfrac{51}{8}\) = \(6\dfrac{3}{8}\)
問１５
( □ – 11 ) × 0.25 – 3 = 5.25 ÷ 0.125 × \(3\dfrac{2}{3}\) ÷ 7
- 答え
- 111
- 解き方
- ( □ – 11 ) × 0.25 – 3 = 5.25 ÷ 0.125 × \(3\dfrac{2}{3}\) ÷ 7
( □ – 11 ) × \(\dfrac{1}{4}\) – 3 = \(\dfrac{21}{4}\) ÷ \(\dfrac{1}{8}\) × \(\dfrac{11}{3}\) × \(\dfrac{1}{7}\)
( □ – 11 ) × \(\dfrac{1}{4}\) – 3 = \(\dfrac{\cancelto{\cancelto{1}{3}}{21}}{\cancelto{1}{4}}\) × \(\cancelto{2}{8}\) × \(\dfrac{11}{\cancelto{1}{3}}\) × \(\dfrac{1}{\cancelto{1}{7}}\) = 22
( □ – 11 ) × \(\dfrac{1}{4}\) = 22 + 3 = 25
□ – 11 = 25 × 4 = 100
□ = 100 + 11 = 111
※覚えておこう！
0.25 = \(\dfrac{25}{100}\) = \(\dfrac{25}{25\ ×\ 4}\) = \(\dfrac{1}{4}\)
0.125 = \(\dfrac{125}{1000}\) = \(\dfrac{25\ ×\ 5}{25\ ×\ 40}\) = \(\dfrac{1}{8}\)
問１６
( 1.25 – \(\dfrac{1}{8}\) ) × ( □ – \(\dfrac{4}{25}\) ÷ 0.075 ) = \(\dfrac{3}{8}\)
- 答え
- \(2\dfrac{7}{15}\)
- 解き方
- ( 1.25 – \(\dfrac{1}{8}\) ) × ( □ – \(\dfrac{4}{25}\) ÷ 0.075 ) = \(\dfrac{3}{8}\)
( \(\dfrac{5}{4}\) – \(\dfrac{1}{8}\) ) × ( □ – \(\dfrac{4}{25}\) ÷ \(\dfrac{3}{40}\) ) = \(\dfrac{3}{8}\)
( \(\dfrac{10}{8}\) – \(\dfrac{1}{8}\) ) × ( □ – \(\dfrac{4}{\cancelto{5}{25}}\) × \(\dfrac{\cancelto{8}{40}}{3}\) ) = \(\dfrac{3}{8}\)
\(\dfrac{9}{8}\) × ( □ – \(\dfrac{32}{15}\) ) = \(\dfrac{3}{8}\)
□ – \(\dfrac{32}{15}\) = \(\dfrac{\cancelto{1}{3}}{\cancel{8}}\) × \(\dfrac{\cancel{8}}{\cancelto{3}{9}}\) = \(\dfrac{1}{3}\)
□ = \(\dfrac{1}{3}\) + \(\dfrac{32}{15}\) = \(\dfrac{5\ +\ 32}{15}\) = \(\dfrac{37}{15}\) = \(2\dfrac{7}{15}\)
※覚えておこう！
1.25 = \(\dfrac{125}{100}\) = \(\dfrac{25\ ×\ 5}{25\ ×\ 4}\) = \(\dfrac{5}{4}\)
0.75 = \(\dfrac{75}{100}\) = \(\dfrac{25\ ×\ 3}{25\ ×\ 4}\) = \(\dfrac{3}{4}\)
0.075 = \(\dfrac{75}{1000}\) = \(\dfrac{3}{40}\)
問１７
30 ÷ \(3\dfrac{3}{4}\) – ( 4 – \(1\dfrac{2}{5}\) ) ÷ □ = \(6\dfrac{2}{3}\)
- 答え
- \(1\dfrac{19}{20}\)
- 解き方
- 30 ÷ \(3\dfrac{3}{4}\) – ( 4 – \(1\dfrac{2}{5}\) ) ÷ □ = \(6\dfrac{2}{3}\)
30 ÷ \(\dfrac{15}{4}\) – \(2\dfrac{3}{5}\) ÷ □ = \(\dfrac{20}{3}\)
\(\cancelto{2}{30}\) × \(\dfrac{4}{\cancel{15}}\) – \(\dfrac{13}{5}\) ÷ □ = \(\dfrac{20}{3}\)
8 – \(\dfrac{13}{5}\) ÷ □ = \(\dfrac{20}{3}\)
\(\dfrac{13}{5}\) ÷ □ = 8 – \(\dfrac{20}{3}\) = \(\dfrac{24\ -\ 20}{3}\) = \(\dfrac{4}{3}\)
\(\dfrac{4}{3}\) × □ = \(\dfrac{13}{5}\)
□ = \(\dfrac{13}{5}\) × \(\dfrac{3}{4}\) = \(\dfrac{39}{20}\) = \(1\dfrac{19}{20}\)
問１８
\(1\dfrac{1}{2}\) × \(4\dfrac{1}{6}\) ÷ ( \(\dfrac{3}{□}\) – \(1\dfrac{1}{2}\) ) = 2.5
- 答え
- \(\dfrac{3}{4}\)（ または 0.75 ）
- 解き方
- \(1\dfrac{1}{2}\) × \(4\dfrac{1}{6}\) ÷ ( \(\dfrac{3}{□}\) – \(1\dfrac{1}{2}\) ) = 2.5
\(\dfrac{3}{2}\) × \(\dfrac{25}{6}\) ÷ ( \(\dfrac{3}{□}\) – \(\dfrac{3}{2}\) ) = \(\dfrac{5}{2}\)
\(\dfrac{\cancel{3}}{2}\) × \(\dfrac{25}{\cancelto{2}{6}}\) ÷ ( \(\dfrac{3}{□}\) – \(\dfrac{3}{2}\) ) = \(\dfrac{5}{2}\)
\(\dfrac{25}{4}\) ÷ ( \(\dfrac{3}{□}\) – \(\dfrac{3}{2}\) ) = \(\dfrac{5}{2}\)
\(\dfrac{5}{2}\) × ( \(\dfrac{3}{□}\) – \(\dfrac{3}{2}\) ) = \(\dfrac{25}{4}\)
\(\dfrac{3}{□}\) – \(\dfrac{3}{2}\) = \(\dfrac{\cancelto{5}{25}}{\cancelto{2}{4}}\) × \(\dfrac{\cancel{2}}{\cancel{5}}\) = \(\dfrac{5}{2}\)
\(\dfrac{3}{□}\) = \(\dfrac{5}{2}\) + \(\dfrac{3}{2}\) = \(\dfrac{8}{2}\) = 4
4 × □ = 3
□ = 3 ÷ 4 = \(\dfrac{3}{4}\)
問１９
( \(\dfrac{3}{4}\) + □ ) ÷ 0.4 + \(1\dfrac{1}{3}\) = 6
- 答え
- \(1\dfrac{7}{60}\)
- 解き方
- ( \(\dfrac{3}{4}\) + □ ) ÷ 0.4 + \(1\dfrac{1}{3}\) = 6
( \(\dfrac{3}{4}\) + □ ) ÷ \(\dfrac{2}{5}\) + \(1\dfrac{1}{3}\) = 6
( \(\dfrac{3}{4}\) + □ ) ÷ \(\dfrac{2}{5}\) = 6 – \(1\dfrac{1}{3}\) = \(4\dfrac{2}{3}\) = \(\dfrac{14}{3}\)
\(\dfrac{3}{4}\) + □ = \(\dfrac{14}{3}\) × \(\dfrac{2}{5}\) = \(\dfrac{28}{15}\)
□ = \(\dfrac{28}{15}\) – \(\dfrac{3}{4}\) = \(\dfrac{112\ -\ 45}{60}\) = \(\dfrac{67}{60}\) = \(1\dfrac{7}{60}\)
問２０
( \(\dfrac{5}{4}\) + □ ) ÷ \(\dfrac{7}{6}\) – \(\dfrac{1}{2}\) = 1
- 答え
- \(\dfrac{1}{2}\)（ または 0.5 ）
- 解き方
- ( \(\dfrac{5}{4}\) + □ ) ÷ \(\dfrac{7}{6}\) – \(\dfrac{1}{2}\) = 1
( \(\dfrac{5}{4}\) + □ ) ÷ \(\dfrac{7}{6}\) = 1 + \(\dfrac{1}{2}\) = \(\dfrac{3}{2}\)
\(\dfrac{5}{4}\) + □ = \(\dfrac{\cancel{3}}{2}\) × \(\dfrac{7}{\cancelto{2}{6}}\) = \(\dfrac{7}{4}\)
□ = \(\dfrac{7}{4}\) – \(\dfrac{5}{4}\) = \(\dfrac{2}{4}\) = \(\dfrac{1}{2}\)
問２１
8 ÷ 5 + ( 9 – □ ) ÷ 3 × 2 – 1 = 3
- 答え
- \(5\dfrac{2}{5}\)（ または 5.4 ）
- 解き方
- 8 ÷ 5 + ( 9 – □ ) ÷ 3 × 2 – 1 = 3
\(\dfrac{8}{5}\) + ( 9 – □ ) ÷ 3 × 2 – 1 = 3
( 9 – □ ) ÷ 3 × 2 = 3 + 1 – \(\dfrac{8}{5}\) = \(\dfrac{15\ +\ 5\ -\ 8}{5}\) = \(\dfrac{12}{5}\)
9 – □ = \(\dfrac{\cancelto{6}{12}}{5}\) × 3 × \(\dfrac{1}{\cancel{2}}\) = \(\dfrac{18}{5}\)
□ = 9 – \(\dfrac{18}{5}\) = \(\dfrac{45\ -\ 18}{5}\) = \(\dfrac{27}{5}\) = \(5\dfrac{2}{5}\)
問２２
1 ÷ { 1 + 1 ÷ ( 1 + □ ) } + 1 = \(\dfrac{13}{8}\)
- 答え
- \(\dfrac{2}{3}\)
- 解き方
- 1 ÷ { 1 + 1 ÷ ( 1 + □ ) } + 1 = \(\dfrac{13}{8}\)
1 ÷ { 1 + 1 ÷ ( 1 + □ ) } = \(\dfrac{13}{8}\) – 1 = \(\dfrac{5}{8}\)
（ 1 を何で割ったら \(\dfrac{5}{8}\) になるかを考える ）
1 + 1 ÷ ( 1 + □ ) = \(\dfrac{8}{5}\)
1 ÷ ( 1 + □ ) = \(\dfrac{8}{5}\) – 1 = \(\dfrac{3}{5}\)
1 + □ = \(\dfrac{5}{3}\)
□ = \(\dfrac{5}{3}\) – 1 = \(\dfrac{2}{3}\)
問２３
□ に、+、-、×、÷ のいずれかの記号を入れ、式を完成させなさい。ただし、記号は同じものを何度使用してもよいものとし、使わない記号があってもよいものとします。
234 × 9 □ 6 □ 7 □ 8 □ 1 □ 2 = 2060
- 答え
- 234 × 9 – 6 × 7 – 8 × 1 ÷ 2（ または 234 × 9 – 6 × 7 – 8 ÷ 1 ÷ 2 ）
- 解き方
- ① 最初の大きな固まりを計算する。
234 × 9 = 2106
② 目指す答えとの差を考える。
2106 – 2060 = 46
③ 残りの数「 6 」「 7 」「 8 」「 1 」「 2 」で「 46 」を作る。
・「 6 」「 7 」で「 46 」に近い数を作る。
（ 大きな数を作る ⇒ かけ算、またはたし算 ）
6 × 7 = 42
あと、「 46 」まであと「 4 」必要である。
・「 8 」「 1 」「 2 」で「 4 」を作る。
8 ÷ 2 = 4
（ 「 1 」はかけ算やわり算で消せる！ ）
8 × 1 ÷ 2 = 4 または 8 ÷ 1 ÷ 2 = 4
④ 式を組み立てて確かめる。
・234 × 9 – 6 × 7 – 8 × 1 ÷ 2
= 2106 – 42 – 4 = 2060
・234 × 9 – 6 × 7 – 8 ÷ 1 ÷ 2
= 2106 – 42 – 4 = 2060