Digit sum of 40 = (4 + 0 = 4)
Digit sum of 41 = (4 +1 = 5)
Digit sum of 42 = (4 + 2 = 6)
Digit sum of 43 = (4 + 3 = 7)
Digit sum of 44 = (4 + 4 = 8)
Digit sum of 45 = (4 + 5 = 9)
Digit sum ,of 46 = (4 + 6 = 10)
Digit sum of 47 = (4 + 7 = 11)
Digit sum of 48 = (4 + 8 = 12)
Digit sum of 49 = (4 +9 = 13)
Digit sum of 50 = (5 + 0 = 5)
Digit sum of 51 = (5 + 1 = 6)
Digit sum of 52 = (5 + 2 = 7)
Digit sum of 53 = (5 + 3 = 8)
Digit sum of 54 = (5 + 4 = 9)
Digit sum of 55 = (5 + 5 = 10)
Digit sum of 56 = (5 + 6 = 11)
Digit sum of 57 = (5 + 7 = 12)
Digit sum of 58 = (5 + 8 = 13)
Digit sum of 59 = (5 + 9 = 14)
Digit sum of 60 = (6 + 0 = 6)
Digit sum of 61 = (6 + 1 = 7)
Digit sum of 62 = (6 + 2 = 8)
Digit sum of 63 = (6 + 3 = 9)
Digit sum of 64 = (6 + 4 = 10)
Digit sum of 65 = (6 + 5 = 11)
Digit sum of 66 = (6 + 6 = 12)
Digit sum of 67 = (6 + 7 = 13)
Digit sum of 68 = (6 + 8 = 14)
Digit sum of 69 = (6 + 9 = 15)
Digit sum of 70 = (7 + 0 = 7)
Observations
For numbers 40 to 49, we get
a sequence 4, 5, 6, 7, 8 … 13
For numbers 50 to 59, we get
a sequence 5,6, 7, 8,… 14
For numbers 60 to 69, we get
a sequence 6, 7, 8, 9, 10,,… 15
Here, the sum of the digits of all the numbers from 40 to 70 is present in the numbers from 4 to 15.