What is the default assumption if nothing is specified regarding the new partner's share of profits from the old partners?

The new partner acquires in the profit sharing ratio of old partners

The correct answer is option 4- The new partner acquires in the profit sharing ratio of old partners.

If nothing is specified regarding the new partner's share of profits from the old partners, the default assumption is that the new partner acquires in the profit-sharing ratio from the old partners. 

When new partner is admitted he acquires his share in profits from the old partners. In other words, on the admission of a new partner, the old partners sacrifice a share of their profit in favour of the new partner. But, what will be the share of new partner and how he will acquire it from the existing partners is decided mutually among the old partners and the new partner. However, if nothing is specified as to how does the new partner acquire his share from the old partners; it may be assumed that he gets it from them in their profit sharing ratio.