The simple interest on Rs 10 for 4 months @3 paisa per rupee per month is

1.20 rupee

The formulae for simple interest is as follows:

S.I = PTR/100 = (10 x 4 x 3)/100 = 12/10 = 1.20 rupees.

OR

Simple Interest:

⇒ 3 paisa on Rs.1 in 01 months

⇒ 30 paisa on Rs.10 in 01 months

⇒ 120 paisa on Rs.10 in 04 months

Therefore, answer is 120 paisa or 1.20 rs.