The manufacturing cost of a cell phone was $136. sellers first marked up the cost by 25 percent. sales were poor, so sellers decreased the markup to 17 percent. calculate the old and new selling prices. selling price = original cost + markup value

Manufacturing cost = $136
sellers added 25% = $ 136 * 25/100 = $34 
manufacturers cost + 25% = $136 + $34 = $170. 
old selling price = $170

Sellers decreased the markup to 17% (of manufacturing cost): $136 x 17/100  = $23.12
New selling price = $136 + $23.12 = $153.12

both of these answers show: original cost + markup value