Answer: You may have a number of factors at work ranging from lack of pollination to simply "hot dry weather". You need to keep the plants from being stressed which means ample water (a larger pot might help, note that for next year) and fertility. Be sure to follow the label instructions for active growth or use a fertilizer formulated specifically for tomatoes, and keep in mind that overfertilizing with nitrogen can actually contribute to blossom drop. If your area is windy, try to protect your plant from that because it increases the rate it dries out and causes additional stress. An old method to encourage fruit set is to rattle the plant around noon on a hot sunny day -- but I suspect a change in the weather is what will really do the trick.
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