A Student was asked to multiply a number by 3/2 but he divided that number by 3/2. His result was 10 less than the original answer. The number was:15101220

Let's denote the number as x.

According to the problem, the student was supposed to multiply the number by 3/2, so the correct result should be (3/2)x.

However, the student divided the number by 3/2 instead, which gives the result as (2/3)x.

The problem states that the student's result was 10 less than the correct result. So, we can set up the following equation:

(3/2)x - 10 = (2/3)x

To solve for x, first we can get rid of the fractions by multiplying the entire equation by 6. This gives:

9x - 60 = 4x

Subtract 4x from both sides to get:

5x = 60

Finally, divide both sides by 5 to solve for x:

x = 60/5 = 12

So, the original number was 12.