Ben and John had 270 dollars all together. Ben decided to give a quarter of what he had in exchange for a third of what John had. As a result of the exchange, they both had an equal amount of money. How did they have at first? 中学2年レベルの数学ではないか。。。こんなtoughな問題、x と y を使わなければとても解くことができない。他の子供たちは本当にこんな問題を解けるのだろうか。。。と思いつつ、私は春休みの1週間で彼女に方程式の基本をたたきこんだ。