Aruna is sitting at first position (say from left end) of the row. There are 8 girls between Aruna and Bimla, ⇒ Bimla is sitting at 10th position. Now, there are 14 girls after Chetna, for number of girls to be minimum, Chetna must sit to the left of Bimla, ⇒ Chetna's position = 4th from left end ∵ There are 14 more girls, thus minimum number of girls = 4 + 14 = 18