Optics confusion PLESE HELP!!!!!?

2 convex lens of focal length 10 cm each are placed at a separation of 15 cm with the principle axes coinciding.The question asked the focal length of the system.The answer is positive using the formula 2/f - d/(f*f) which is correct too.The problem that i have is that the system is behaving like a diverging lens for a distant object.There is also a note below the question telling this fact.So why is the system behaving like a diverging lens though its focal length is +ve.PLEASE HELP!!!!!!!!!!!!!! THANKS FOR TRYING