Percentage Decrease in Area =(( Original Area - New Area )∕ Original Area )×100 Calculation: Original Area =L×B New Area =0.7L×0.9B New Area =0.63LB Percentage Decrease in Area =((L×B−0.63LB)∕L×B)×100 ⇒ Percentage Decrease in Area =((LB−0.63LB)∕LB)×100 ⇒ Percentage Decrease in Area =(0.37LB∕LB)×100 ⇒ Percentage Decrease in Area =0.37×100 ⇒ Percentage Decrease in Area =37%