This paper analyzes the design problem of a paired-line hybrid transit system in a monocentric city with a densely populated central business district (CBD). The trip production rate is assumed to decrease exponentially with increasing distance from the city center. As to the trip distribution, two different areas, the CBD and the rest of the city, are identified. Trips ending in each area are homogeneously distributed within that area but their proportions in the total trips are distinctive to model the heterogeneity in trip distribution. To address the challenge of estimating system costs analytically under the above exponential demand pattern, new approximation methods are proposed and validated using a Monte Carlo simulation. Results of numerical experiments show that the exponential demand pattern helps reduce the cost of paired-line hybrid transit systems in monocentric cities, with a saving up to 20% when both the trip production and distribution are heavily concentrated in the CBD. Furthermore, strong quadratic/linear relationships are found between the parameters controling demand concentration level and the system cost. The proposed model can guide the design of hybrid transit systems in monocentric cities with a demand pattern similarly structured as considered in this study.