A dealer of scientific instruments allows 20% discount and still makes a profit of 25%. If his gain on sale of an instrument is ₹ 150, then find the marked price of the instrument.

₹ 937.50

Let C.P of instrument =Rs.100

We have,

Profit =25% of Rs.100 = Rs.25

If profit is Rs.25,

C.P=Rs.100

∴ If profit is Rs.150,

C.P = Rs.100/25×150=Rs.600

S.P of the instrument  =Rs.600 + Rs.150 = Rs.750

Let M.P of the instrument be Rs. 100

If S.P is Rs.80, M.P = Rs.100/80 × 750 = Rs.937.50

Thus, marked price of the instrument =Rs.937.50