The average age of eight girls is y years. 5 new girls having ages (in years) given by y + 3, y - 6, y + 15, y + 8, and y + 6, join the class. What is the new average age of the class?

(y + 2) years

Sum of age of 8 girls = 8y

Sum of age of 13 girls = 8y +( y+3 )+ (y-6) +( y+ 15) + (y+ 8) +( y + 6 )

= 13y + 26

New Average = \(\frac{13y + 26}{13}\) = ( y + 2 ) years