Assume that the fruit seller had 100 apples initially.
He sell 40% of them = 40 apples
Left out apples = (100 – 40) = 60
In initial amount of apples if 60 of them are remaining = 100
In initial amount of apples if 1 of them is remaining = (100/60)
In initial amount of apples if 420 of them are remaining = (100/60) × (420)
= (100 ×7)
= 700
∴the fruit seller originally had 700 apples.