15 is already a whole number, so rounding it would still give 15. Perhaps you meant what range of numbers would round to 15. The answer, in words, is all numbers that lie between 14.5 and up to but not including 15.5. This can be written mathematically in two ways: [14.5,15.5) as an open-ended interval; or as an inequality where n is the number: 14.5≤n<15.5.