Gain or loss on the sale of a partnership interest is allocable to this state in the ratio of the original cost of partnership tangible property in the state to the original cost of partnership tangible property everywhere, determined at the time of the sale. In the event that more than fifty percent of the value of the assets of the partnership consist of intangibles, gain or loss from the sale of the partnership interest is allocated to this state in accordance with the ratio of total North Dakota income to total income of the partnership for its first full tax period immediately preceding the tax period of the partnership during which the partnership interest was sold. This section applies to the extent, that prior to the sale of the partnership interest, the partnership’s income or loss constituted nonbusiness income.