Pen, Pencil, and Rubber in a box are in proportion to 3: 2: 1. If the value of pen, pencil and rubber is Rs.3, Rs.2 and Rs.2, respectively, and the total amount spent on the entire box is Rs.840, then find out the number of pens in the box.

Let the ratio of pen, pencil, and rubber in the box be 3x: 2x: x (since the ratio is given as 3:2:1). Let the value of a pen, pencil, and rubber be Rs. 3, Rs. 2, and Rs. 2, respectively. Then, the amount spent on the box can be calculated as: Amount spent = (value of a pen x 3x) + (value of a pencil x 2x) + Amount spent = (3 x 3x) + (2 x 2x) + (2 x x) [substituting the given Amount spent = 9x + 4x + 2x Amount spent = 15x It is given that the amount spent on the box is Rs. 840. So, we have: 15x = 840 x = 56 Therefore, the ratio of pen, pencil, and rubber in the box is 3x: 2x: x = 168:112:56.   So, the number of pens in the box is 168.