In an experiment, lab rats are put in a cage in which there is a lever. The rats "learn" to push the lever, after which they are rewarded with a food pellet. It has been determined that 90% of the time, the rats "learn" to push the lever after they have been put in the cage. Suppose 45 rats are placed in cages with levers.

Q1: Find the standard deviation of the number of rats that will learn to push the lever. (Round your answer to two decimal places.)