At West painting, they get about three calls a day asking for estimate of the cost for having the interior of a house painted to write up an estimate for the cost of a job they need to know how much paint a job will take if they average painting 3/4 of a room with 2/5 of a gallon of paint when they can paint on average blank rooms per gallon

To determine the amount of paint required for a job, we can use the given information:

- They average painting 3/4 of a room with 2/5 of a gallon of paint.
- They can paint on average blank rooms per gallon.

Let's calculate the amount of paint needed for 1 room:

Paint required for 3/4 of a room = (3/4) * (2/5) = 6/20 = 3/10 gallon

Now, we need to find out how many rooms can be painted with 1 gallon of paint:

Rooms per gallon = 1 / (3/10) = 10/3 = 3.33 (approx.)

Since we can't paint a fraction of a room, we can conclude that on average they can paint 3 rooms per gallon of paint.

Therefore, when writing up an estimate for the cost of a job, West painting needs to consider that an average job will require 1 gallon of paint.