Two thin lenses of power + 4D and –2D are in contact.

power 4dPower ToTo 655. Pick 6 of your favourite numbers from 1 to 55, each bet is RM1. Supreme ToTo 658. Pick 6 of your favourite numbers from 1 to 58, each bet is RM2.6. A convex lens of power +6 D is placed in contact with a concave lens of power –4D. What will be the nature and focal length of this combination ? (a) convex, 100 cm (b) convex, 50 cm