If a number a is a 2 digit number and its digits are transposed to form number b, then the difference between the larger of the two numbers and the smaller of the two numbers must be divisible by:

An automated water dispenser fills packets with one liter of water on average, with a standard deviation of 5 milliliter. the manual says that after a year of operation the dispenser should be tested to see if it needs recalibration. a year later a number of filled packets are set aside and measured separately. it is found that the average packet now contains about 0.995 liters. does the dispenser need calibration? explain your answer.

Can someone check if i did this correct. it’s number 4 if you’re wondering.

45% of the trees in a park are apple trees. there are 27 apple trees in the park. how many trees are in the park in all?