Markup is calculated by dividing the difference between the selling price and the cost by the cost. In this case, the markup is (\frac{100-50}{50}) = 100%.

Selling price is calculated by adding the markup to the cost. In this case, the selling price is (50 + 50\cdot0.50) = \$75.

Cost is calculated by dividing the selling price by 1 plus the markup percentage. In this case, the cost is (\frac{100}{1+0.25}) = \$80.

Markup percentage is calculated by dividing the difference between the selling price and the cost by the cost. In this case, the markup percentage is (\frac{120-90}{90}) = 33.33%.

Selling price is calculated by adding the markup to the cost. In this case, the selling price is (75 + 75\cdot0.20) = \$90.

Cost is calculated by dividing the selling price by 1 plus the markup percentage. In this case, the cost is (\frac{150}{1+0.40}) = \$107.14.

Markup percentage is calculated by dividing the difference between the selling price and the cost by the cost. In this case, the markup percentage is (\frac{200-120}{120}) = 66.67%.

Selling price is calculated by adding the markup to the cost. In this case, the selling price is (100 + 100\cdot0.30) = \$130.

Cost is calculated by dividing the selling price by 1 plus the markup percentage. In this case, the cost is (\frac{250}{1+0.50}) = \$166.67.

Markup percentage is calculated by dividing the difference between the selling price and the cost by the cost. In this case, the markup percentage is (\frac{300-200}{200}) = 50%.

Selling price is calculated by adding the markup to the cost. In this case, the selling price is (150 + 150\cdot0.40) = \$210.

Cost is calculated by dividing the selling price by 1 plus the markup percentage. In this case, the cost is (\frac{350}{1+0.60}) = \$218.75.

Markup percentage is calculated by dividing the difference between the selling price and the cost by the cost. In this case, the markup percentage is (\frac{400-250}{250}) = 60%.

Selling price is calculated by adding the markup to the cost. In this case, the selling price is (200 + 200\cdot0.50) = \$300.

Cost is calculated by dividing the selling price by 1 plus the markup percentage. In this case, the cost is (\frac{450}{1+0.70}) = \$264.71.