This is exactly how luni-solar calendars, such as the hebrew or the chinese one work. using various schemes, these calendars add x months (you’ll find x in part (c)) over the period of 12 ∗ 19 = 228 synodic months to get the total that is almost exactly equal in length to 19 solar years. that way those calendar are average synchronized with the gregorian calendar. (e) (optional) a purely lunar calendar, such as the islamic one, does not synchronize with the solar year. because of this, muslim holidays tend to drift from year to year relative to the gregorian calendar. after a number of years they will make a full circle through the gregorian calendar. how many lunar years will pass till the difference accumulates to more than one solar year?

Researchers conducted an experiment to identify the effects of three different hand sanitizers on the growth of bacteria. the researchers grew one type of bacteria in twenty-four identical covered petri dishes. then, they opened eighteen petri dishes and applied the three hand sanitizers to six petri dishes each. they left the remaining six petri dishes closed as a control group. when the researchers measured the growth of bacteria two days later, the six dishes that had no hand sanitizer showed the least amount of bacterial growth. the researchers concluded that not using any hand sanitizer would lead to the least bacterial growth. which statement best explains why the researchers’ conclusion was not justified? the experiment tested too many variables. the control group was not treated the same as the experimental group. the sample size of twenty-four petri dishes is not large enough. the single type of bacteria is not adequate to make any conclusions.