The average age of 8 students is 20. The average age of first two students is 19 and that of the next three students is 21. If the age of the sixth student is less than that of the seventh and eighth student by 2 and 3 respectively, then find the age of the eighth student.
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average age of 8 students =20
sum of ages of 8= 20×8 =160
average age of first 2 students = 19
sum of ages of first 2= 19×2 =38
average age of next 3 = 21
sum of ages of next 3 = 21×3 =63
age of 7-age of 6= 2
=> age of 7th = 2+ age of 6th
age of 8- age of 6 =3
=> age of 8th = 3+ age of 6th
sum of ages of 6th, 7th and 8th students
=160-(38+63) = 160- 101 = 59
=> 2+age of 6th +3+age of 6th +age of 6th =59
=5+3×age of 6th =59
=3×age of 6th = 54
=> age of 6th = 18 years
age of 8th student = 18+3 = 21
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