Question

convex lens produces an inverted magnified 3 times of an object placed at a distance of 15 cm from the calculate focal length of it

Answer 1

first find v that is image distance.....v= 45
Using lens formula... 1/f=1/v-1/u
1/f=4/45
f=45/4=11.2

Answer 2

m = -3 (inverted)

u = -15cm

m = v/u = v/-15

-3 = v/-15

v = 45cm

Using lens formula: 1/v - 1/u = 1/f

1/f = 1/45 - 1/-15

1/f = 1+3/45 (taking LCM)

1/f = 4/45

f = 11.25cm