Where an employee performs work during his workweek, some of which is exempt under one section of the Act, and the remainder of which is exempt under another section or sections, of the Act, the exemptions may be combined. The employee's combination exemption is controlled in such case by that exemption which is narrower in scope. For example, if part of his work is exempt from both minimum wage and overtime compensation under one section of the Act, and the rest is exempt only from the overtime pay requirements by virtue of section 7(b)(3), the employee is exempt that week from the overtime pay provisions, but not from the minimum wage requirements. Similarly, an employee who spends part of his workweek in work which would, if done throughout the week, exempt him completely from the overtime pay requirements, and the remainder of the week in work exempt from such requirements only to the extent and under the conditions specified in section 7(b)(3), could be exempt from overtime pay only to such extent and under such conditions. Thus where an employee spends part of his workweek in transporting petroleum products by tank truck for an employer in an enterprise described in section 7(b)(3), and the remainder of his workweek in driving a taxicab for the employer's taxi business (work exempt from the overtime provisions under section 13(b)(17)), he is eligible for exemption from overtime pay only if he is compensated in such workweek in accordance with the provisions of section 7(b)(3) and only to the extent which that section provides.