Answers

2016-01-10T14:40:47+05:30
Percentage of students who won prizes = 10+12%=22%. 22%of 30,000 won prizes, i.e. 22/100×30,000= 6,600 students. -> 22% students won prizes which in number are 6,600 students out of 30,000.
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Sorry !!!
2016-01-10T14:51:58+05:30
Total no.of students = 30,000
No.of girl participants = 40% of 30,000
                                   = (40/100) × 30,000
                                   = (2/5)×30,000
                                   = 12000
No.of boy participants = 30,000 - 12000
                                    = 18000
no.of winners in boys = 10% of no.of boys
                                    = (10/100)×18000
                                    = 1/10  × 18000
                                    = 18000/10
                                    = 1800
no.of winners in girls = 12% of no.of girls 
                                   = (12/100) × 12000
                                   = (3/25)  × 12000
                                   = 1440
Total no.of winners  = 1800 + 1440  = 3240
∴ Percentage of students who won the prize = (3240/30000) ×100     
                                                                      = 10.8%
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