★★★☆☆中級コース　1行計算問題ラサール中学入試問題より

2.5
ラサール中学　2020年入試問題より

【問題１】　\(\displaystyle\frac{1}{8}\)×(2\(\displaystyle\frac{7}{9}\)+\(\displaystyle\frac{9}{11}\)ー\(\displaystyle\frac{5}{81}\))ー\(\displaystyle\frac{9}{88}\)

【ヒント】（　）をはずして、帯分数を仮分数にし、１つ１つ丁寧にほぐして解いていきます。

【解答】\(\displaystyle\frac{1}{8}\)×\(\displaystyle\frac{25}{9}\)+\(\displaystyle\frac{1}{8}\)×\(\displaystyle\frac{9}{11}\)ー\(\displaystyle\frac{1}{8}\)×\(\displaystyle\frac{25}{81}\)ー\(\displaystyle\frac{9}{88}\)=\(\displaystyle\frac{1×25}{8×9}\)ー\(\displaystyle\frac{1×25}{8×81}\)=\(\displaystyle\frac{25}{8×81}\)(9ｰ1)
=\(\displaystyle\frac{25}{81}\)　　・・・（答え）

【問題2】19.9－1.4×（2.7＋ア）＝10.8

【ヒント】左の辺と右の辺に10をかけます。

【解答】199－14（\(\displaystyle\frac{27}{10}\)+ア)=108

14（\(\displaystyle\frac{27}{10}\)+ア)=199ｰ108

（\(\displaystyle\frac{27}{10}\)+ア)=\(\displaystyle\frac{91}{14}\)

ア＝\(\displaystyle\frac{13}{2}\)ー\(\displaystyle\frac{27}{10}\)

=\(\displaystyle\frac{65-27}{10}\)=\(\displaystyle\frac{38}{10}\)=3.8 ・・・（答え）

【問題３】57×15.2ー114×2.6＋４×3.25＝？

【解答】57×\(\displaystyle\frac{152}{10}\)ー114×\(\displaystyle\frac{26}{10}\)＋４×３\(\displaystyle\frac{1}{4}\)=\(\displaystyle\frac{57×76}{5}\)ｰ\(\displaystyle\frac{57×2×13}{5}\)＋４×\(\displaystyle\frac{12＋1}{4}\)

＝\(\displaystyle\frac{57}{5}\)×（76－２×13）＋13

＝\(\displaystyle\frac{57}{5}\)×５０＋13

＝570＋１３＝583・・・（答え）