If selling and administrative expenses decrease while other expenses remain constant, what will happen to return on investment (ROI) ?

The ROI will increase.

Explanation:

ROI (Return on investment) is concept which is used by the management of a corporation to evaluate a project and to see how profitable a project would be and on the basis of profitability, that project would be accepted or rejected. If the selling and administrative expenses decreases, given that other expenses remains same, it means that there will be decrease in operating expenses, which means the ROI would increase.