The average age of 35 persons is 40 years. 5 new persons with an average age of 35 years joined them. The average age of all the persons is:

$39\frac{3}{8}$ years

Sum of age of 35 person = 35  × 40 = 1400 years

After joining 5 persons of 35 years ,

Sum  of 40 persons = 1400 + 5  × 35 = 1400 + 175 = 1575 years

Average of all = \(\frac{1575 }{40}\) = 39\(\frac{3}{8}\) years