Answer:
d = 690 cm
Step-by-step explanation:
The complete question is:
An optician's test card is fixed at 90 cm behind the eyes of a patient who looks into a plane mirror which is at 300 cm in front of him as shown in the Mirror. At what distance is the card seen by the patient?
So, first of all we need to find the distance between the mirror and the chart. Since, the distance between mirror and person is 300 cm, while the distance between the same person and test card is 90 cm. So, the total distance between the test card and mirror will be 300 cm + 90 cm = 390 cm.
Hence, the image formed of test card in the mirror will be 390 cm behind the mirror. So, in order to find the distance between the person and the image of test card we have to add the distance between person (300 cm) and mirror to this value.
distance between person and image of card = d = 390 cm + 300 cm
d = 690 cm