It is known that 25% of 11-year-old children have no decayed, missing, or filled (dmf) teeth. in a sample of 10 children, find the probability that exactly 3 have no dmf teeth.

Okay, so if these 10 Sample children are all 11 years old, you want to find out how much one percent of ten is. 0.01, which translates into one percent, is multiplied by ten. This gives you .10 children for every one percent. Now, you should figure out how many times .10 goes into three, which is thirty. Multiply 1 percent by thirty to get you 30 percent, the probability that out of 10 eleven year olds, three have no dfm teeth.