Many tests that purport to measure intelligence are timed. The decision of how much time to allow for such a test often is made after examination of samples of times for completion of practice...

Extracted text: Many tests that purport to measure intelligence are timed. The decision of how much time to allow for such a test often is made after examination of samples of times for completion of practice versions of the test. Below is a histogram summarizing 64 such times for completion for one type of test. Frequency 30+ 28 25- 20 20- 15- 10- 4 4 5+ 16 Time for completion (in minutes) 12 20 24 28 Based on this histogram, estimate the standard deviation of the sample of 64 times. Carry your intermediate computations to at least four decimal places, and round your answer to at least one decimal place. (If necessary, consult a list of formulas.)