The bus started with 50 people – 15 who got off at the first stop = <<50-15=35>>35 people on the bus.
At the second stop, 35 people on the bus – 8 who got off = <<35-8=27>>27 people.
Then there were 27 people + 2 who got on = <<27+2=29>>29 people on the bus.
At the third stop, 29 people on the bus – 4 who got off = <<29-4=25>>25 people on the bus.
Then there were 25 people on the bus + 3 who got on = <<25+3=28>>28 people on the bus.
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