1) Number of students = 30
Number of girls = 60% x 30 = (60 x 30) /100 = 18
Hence number of boys = Number of students - Number of girls = 30 - 18 = 12 Ans
2) Selling price = 8100
Loss = 10%
SP x 100 8100 x 100 8100 x 100
Cost Price = ---------------- = ----------------- = -------------- = 90 x 100 = 9000
(100 - loss%) 100 - 10 90
Ans. Rs 9000
OR
Selling price = 8100
Loss = 10%
If SP is 100 then CP = 100-10 = 90
if SP is 1 then CP = 90/100
if SP is 8100 then CP = 90 x 8100 / 100 = 9000 Ans.