A subnet's range is determined by its network address and subnet mask. The range starts with the lowest address (all host bits set to 0) and ends with the highest address (all host bits set to 1). The highest address is the broadcast address.
Example
Your CIDR is 10.200.20.0/24. The 24 means the first 24 bits of the netmask comprise the network address. That leaves 8 bits leftover for the host portion. (IPv4 addresses have 32 bits. 32 - 24 = 8.)
The netmask looks like this:
255.255.255.0
Or, in binary:
11111111.11111111.11111111.00000000
We can figure out how may hosts the netmask supports by calculating the number of combinations we can make out of 8 bits. We do that using exponentiation.