Question

A shopkeeper buys a number of packets of biscuits for rupees 80.Had he bought 4 more packets for the same amount, each packet would have cost rupees 1 less.How many packets did he buy?

Answer 1

let the no of packets be x 
let the cost of each packet be y

so xy = 80 ⇒ y = 80/x

so if he would have bought 4 more packets for the same amount, each packet would have cost rupees 1 less  (x+4)(y-1)=80

⇒ (x+4)(80/x-1)=80

⇒ x² + 4x - 320 = 0

⇒ x² + 20x - 16x - 320 = 0

⇒ (x - 16)(x + 20) = 0

so x = 16 or - 20 

so number of packets can't be negative
so 16 packets he bought ANSWER

Answer 2

HERE IS UR ANSWER

let the no of packets be x 

let the cost of each packet be y

so xy = 80 ⇒ y = 80/x

so if he would have bought 4 more packets for the same amount, each packet would have cost rupees 1 less  (x+4)(y-1)=80

⇒ (x+4)(80/x-1)=80

⇒ x² + 4x - 320 = 0

⇒ x² + 20x - 16x - 320 = 0

⇒ (x - 16)(x + 20) = 0

so x = 16 or - 20 

so number of packets can't be negative

16 packets