A bank randomly surveyed 50 of its customers by mail to find out how customers use its mobile banking service. The survey found that only 11 of the 50 customers used the service.

If the branch has 1,700 customers, about customers use the mobile banking service.

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To answer the problem above, use the concept of ratio and proportion. By letting x be the number of customers using the mobile banking service, the proportion may be expressed as,

11 / 50 = x / 1,700

Solving x gives x = 374. Thus, out of 1700 customers, 374 use the mobile banking service.