Bolt charges dubious.

How do Bolt calculate their fares? We seem to find this problem regularly with them . My husband and I both requests rides from them with 2 phones, sitting next to each other. Sometimes there is more than R10 difference for 2 people going to the same place at the same time. Today I checked again I have a 10% discount my husband no discount but the amount is exactly the same. How can this be?