What is the average of numbers from 1 to 50 which are multiples of 2 or 5? (correct to one decimal place)

25.8

For 2

Number of terms → 50 = 2 + 2n - 2

⇒ n = 25

Average = \(\frac{2 + 50}{2}\) = 26   {Average = (1st term + last term ) / 2 }

Total = 26 x 25 = 650

For 5

Number of terms → 50 =5 + 5n - 5

⇒ n = 10

Average = \(\frac{5 + 50}{2}\) = 27.5

Total = 27.5 x 10 = 275

10, 20, 30, 40 and 50 come two times

Effective total = 650 + 275 - 150 = 775

Number of terms which are multiples of 2 or 5 = 25 + 10 - 5 = 30

Average = \(\frac{775}{30}\) = 25.8