What is the average of numbers from 1 to 50 which are multiples of 2 or 5? (correct to one decimal place)
Answer & explanation
Correct answer: option 2
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