1.286 is the same as saying 1.286/1. However, that is not the final answer, because we must simplify the fraction to get rid of the decimal point in the numerator. To do this, we must move the decimal point of 1.286 to the right three places, so that it will occur right after the '6'. To do this, we must multiply both the numerator AND denominator by 10^x (10 to the power of x). The variable x is the amount of places we need to move the decimal point, which is 3 in this case. So we multiply the numerator and denominator by 10^3, which is 1,000.
Once we do that, we get 1,286/1,000. This is technically the final answer, but only some teachers will accept it in this form. Others may ask to put it in mixed fraction form. In this case, we must divide the numerator by denominator. To do this, we'd ask ourselves "how many 1,000's can fit in 1,286?", because the numerator, 1286, is being divided by the denominator, 1000. Only one of '1000' can fit in '1286', and will give a remainder of 286/1000.
So your mixed fraction would be 1 + 286/1000. However, we can simplify this even further. Both '286' and '1000' have a common number that they can both get divided by, which is 2. Dividing both numbers by 2, our final answer will then become 1 + 143/500.
