How many 5element DNA 4bases ACGT sequences a Are there in t

How many 5-element DNA (4-bases ACGT) sequences

a) Are there in total? b) Do not contain thymine? C) Contain the sequence CAT?

Total number of 5-element DNA (4-bases ACGT) sequences = 4×4×4×4×4 = 1024 Do not contain thymine (i.e., Now we have only three bases), hence 3×3×3×3×3 = 243 Contain Sequence CAT = 1×1×1×4×4 = 16