a school has 20 classrooms one-fourth of them are for kinder and first grade. twice as many are for second and third grade. the rest are for fourth and fifth grade. how many fourth and fifth grade classes are there?

The birth weights of newborn babies in the unites states follow in a normal distrubution with a mean of 3.4 kg and standard deviation of 0.6 kg. reaserches interested in studying how. children gain weights decide to take random samples of 100 newborn babies and calculate the sample mean birth weights for each sample