Respuesta :

Ningwa

Answer:

Rs 800

Step-by-step explanation:

Selling Price =Rs640

Loss=20%

Let the cost price of the watch be Rs x.

SP=CP-20%of CP

or, 640=x-x/5

or, 640=4x/5

or, 4x=640*5

or,x=3200/4

Therefore, x=Rs 800. The cost price of the watch is Rs 800.