Then draw a supply curve that intersects the demand curve at a low price. Intuitively, you need to think in terms of marginal analysis. Low prices of medicine mean large quantities of medicine demanded. Demand exceeds supply. There would be a shortage of 70 units.
Supply exceeds demand.
There would be a surplus of 100 units. The demand for large cars would increase - they are now cheaper to drive per mile. The demand for small cars would decrease, because people are shifting to larger cars instead. The demand for hotels would increase, because it is now cheaper to travel. Supply of ice cream increases - it is now cheaper to make a given quantity of ice cream, so suppliers will sell more at every price.