On Tuesday, Oliver worked out for 4 - 2 = <<4-2=2>>2 hours.
On Wednesday he decided to work out twice as much as on Monday, so for 2 * 4 = <<2*4=8>>8 hours.
On Thursday, at home, Oliver trained twice as much as on Tuesday, so for 2 * 2 = <<2*2=4>>4 hours.
In total Oliver trained for 4 + 2 + 8 + 4 = <<4+2+8+4=18>>18 hours.
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