A fruit seller had some oranges. He sold 30% oranges and still had 210 oranges. The number of oranges he had, initially, was:

Let the initial number of oranges the fruit seller had be x (which is 100%).
He sold 30% of the oranges, so the percentage of oranges remaining with him is:

Remaining %=100%−30%=70%
According to the question, he still has 210 oranges:

70% of x=210
100
70
​
×x=210
0.7x=210
x=
0.7
210
​
=
7
2100
​
=350
Therefore, he initially had 350 oranges.