Final answer:
The missing number "S" in the sequence 45, 9, 1.8, S is 0.36.
Step-by-step explanation:
To find the missing number "S" in the sequence 45, 9, 1.8, S, we can observe that each number is getting divided by 5. So, to find "S", we need to divide the previous number (1.8) by 5.
Dividing 1.8 by 5 gives us the value of 0.36. Therefore, the missing number "S" in the sequence is 0.36.