Explanation:
the average is also called the mean value.
it is simply all values added and then dividend by the number of values.
10 1/7 = (10×7 + 1)/7 = 71/7
5 1/3 = (5×3 + 1)/3 = 16/3
2 5/21 = (2×21 + 5)/21 = 47/21
3 4/7 / (3×7 + 4)/7 = 25/7
to be able to truly compare and outright add them, we need to bring these fractions to the same denominator :
the smallest common multiple of 3, 7 and 21 is ... 21.
71/7 = 71/7 × 3/3 = 213/21
16/3 = 16/3 × 7/7 = 112/21
47/21 = 47/21
25/7 = 25/7 × 3/3 = 75/21
the mean value for these 4 digits is now ;
(213/21 + 112/21 + 47/21 + 75/21)/4 =
= 447/21 / 4/1 = 447/84 =
= 149/28 = 5 9/28