I have installed Linux mint on my laptop and now i want to install another OS win 10 (want to keep both). When i installed Linux i made partitions asI want to install win 10 on sda4. Previously when i tried to install win 10 it gave an error(cant install partition must be formatted using ntfs). I am new and need help how can i do that. 
install dual OS
linux mint
You can accomplish this by trying the mkntfs that will create a ntfs partition on the device that you indicate.Then in the case of your notebook...