If the person can't accommodate and the glasses is + 2.50d, at which distance will the person see clearly

When a person is about 40-50 years old, the ability to accommodate has been lost at all. From then on, the “add” determines your point of best focus and having the focal length of a +2.50D lens means that the person can see clearly at 2/5 meter. 

Moreover, in a positive diopter measurement, use 1 as the numerator to find the distance in meters then take the value of 2.5 and make it the denominator. Then, you will have1/2.5, which is equal to 2/5 of a meter.

P= + 2.50  

f = 1/p = 1/+2.50 = 100/2.50  

f = 40 cm                                                                                                                                                               200/5 = 40cm

To a + diopter estimation is a shortsighted man know the amount of 2.5 and give it the denominator with 1 as the numerator to obtain the distance in meters that they can recognize definitely beyond their face 1/2.5 .