Cost is directly proportional to the number of articles.

The cost of production of a certain instrument is directly proportional to the number of units produced. The cost of production for 300 units is $300. What is the cost of production for 270 units?

Work done is directly proportional to the number of men working on it.

Pressure is directly proportional to

A heart is broken is number of feeling 1:2:3:4 .The cost heart is directly proportional to the square of number of fellings .There is loss of Rs. 700 on broken heart .Find the initial cost of the heart ?

Show that the radius of Bohr's orbit is directly proportional to the square of the principal quantum number.

Pressure is directly proportional to the area of contact.