The ratio of the number of boys to that of girls in a school is 5 : 2. If 87% of the boys and 80% of the girls passed in the annual exams, then find the percentage of students who failed in the annual exams.

15%

Given :-

Ratio of ,        Boys   :   Girls 

                         5    :      2

Let Total number of boys  = 50 & Total number of  girls = 20

Passed boys students = 87%

So , Failed boys students = ( 100 - 87 )% = 13%

Number of boys failed = 50 × \(\frac{13}{100}\)  = 6.5

Passed girls students = 80%

So , Failed girls students = ( 100 - 80 )% = 20%

Number of girls failed = 20 × \(\frac{20}{100}\) = 4

Number of failed students  = ( 6.5 + 4) = 10.5

Total number of students = 50 + 20 = 70

Percentage of failed students = \(\frac{10.5}{70}\) × 100 =  15%

So , Number of failed students is 15%