An invoice with the following terms 1/20, n/30 translates as:

		a 1% cash discount may be taken if paid in 20 days; if no cash discount is taken, the balance is due in 30 days after the middle of the month.
		b 1% cash discount may be taken on 20% of the purchase if the account is paid within 30 days after the end of the month.
		c 1% cash discount may be taken if paid in 20 days; if no cash discount is taken, the balance is due 30 days after the end of the month.
		d 1% cash discount may be taken if paid in 20 days; if no cash discount is taken, the balance is due 30 days after the invoice date.