Mrs. Prescott had 21 fiction book and 10 nonfiction books in her classroom library. After she bought some more non-fiction books, mrs. Mrs. Prescott found that one fifth of her library consisted of fiction books. How many non-fiction books did Mrs. Prescott buy?

The decibel level of sound is 50 db greater on a busy street than in a quiet room where the intensity of sound is watt/m2. the level of sound in the quiet room is db, and the intensity of sound in the busy street is watt/m2. use the formula , where is the sound level in decibels, i is the intensity of sound, and is the smallest sound intensity that can be heard by the human ear (roughly equal to watts/m2).

What’s the answer ? use the picture to see the problem

Given: klmn is a parallelogram m? n=3m? k, lf ? kn , ld ? nm kf=2 cm, fn=4 cm find: lf, ld