Question

C = {r:x is a two-digit number sum of whose digits is 4}
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Answer 1

Answer:

C={x:x is a two-digit natural number such that the sum of its digits is 8}

The elements of this set are 17,26,35,44,53,62,71 and 80 only.

Therefore, this set can be written in roster form as C=17,26,35,44,53,62,71,80.