Question

Complete series. 9=4, 21=9, 22=9, 24=10, 8=5, 7=5, 99=10, 100=7 , 16=?, 17=?

Answer 1

16 = 7 and 17 = 9
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The number of letter in the spelling of 16 (sixteen) is 7 and that of 17 (seventeen) is 9

Answer 2

Let see letters.

9 = nine = 4
21 = twenty one = 9
22 = twenty two = 9
23 = twenty three = 10
8 = eight = 5
7 = seven = 5
99 = ninety nine = 10
100 = hundred = 7

So, like that
16 = sixteen = 7
17 = seventeen = 9