Notwithstanding any provision of law to the contrary, all monetary contributions and the equivalent monetary value of properties donated, granted or bestowed to non-stock and non-profit institutions are tax-exempt and deductible from the taxable income of the donor: Provided, That such donations, grants, endowments or contributions shall be used actually, direclty, and exclusively for the primary educational purposes of the recipient: Provided, further, That not more than twenty-five (25) percent of the donations, grants, endowments or contributions shall be used for administrative purposes.