Abox contains10 pens, 5 of the pens are red, 4 are balck and 1 are bluem what is the probability of pulling out a black pen first, putting it back into the box, and then pulling a red pen ?

Pulling out a black pen first will grant you a 40% chance of that occurring, then when you put it back the probability of you pulling out a red pen would be 50% so in decimal form these two values would be .40 and .50 multiply these two together you should get .20 or a 20% chance. Also a written fraction would be 1/5, all of which are valid answers.

15 cm is the answer to your question