Interest = Principal × Time × Rate ∕100 Interest =240, Time =4 and Rate =20 ⇒240= Principal ×4×20∕100 Multiply both sides by 100 and simplify 4×20 (80) ⇒240×100=80× Principal Divide both sides by 80 so that Principal can be alone at one side of the equation 240×100∕80= Principal 80 goes into 240,3 times ⇒3×100= Principal ⇒ Principal =300