Problem: In his 1805 mandolin method, Anweisung die Mandoline von selbst zu erlernen nebst einigen Uebungsstucken von Bortolazzi, Bartolomeo Bortolazzi popularised the Cremonese mandolin, which had four single-strings and a fixed bridge, to which the strings were attached. Bortolazzi said in this book that the new wire strung mandolins were uncomfortable to play, when compared with the gut-string instruments. Also, he felt they had a "less pleasing...hard, zither-like tone" as compared to the gut string's "softer, full-singing tone." He favored the four single strings of the Cremonese instrument, which were tuned the same as the Neapolitan.
 How many double strings did the Cremonese Mandolin have?
---
Answer: unanswerable


Problem: Off-grid PV systems have traditionally used rechargeable batteries to store excess electricity. With grid-tied systems, excess electricity can be sent to the transmission grid, while standard grid electricity can be used to meet shortfalls. Net metering programs give household systems a credit for any electricity they deliver to the grid. This is handled by 'rolling back' the meter whenever the home produces more electricity than it consumes. If the net electricity use is below zero, the utility then rolls over the kilowatt hour credit to the next month. Other approaches involve the use of two meters, to measure electricity consumed vs. electricity produced. This is less common due to the increased installation cost of the second meter. Most standard meters accurately measure in both directions, making a second meter unnecessary.
Why is a second meter usually unnecessary to monitor electricity use?
---
Answer: Most standard meters accurately measure in both directions


Problem: Another view, advanced by Richard Dawkins, is that the existence of God is an empirical question, on the grounds that "a universe with a god would be a completely different kind of universe from one without, and it would be a scientific difference." Carl Sagan argued that the doctrine of a Creator of the Universe was difficult to prove or disprove and that the only conceivable scientific discovery that could disprove the existence of a Creator would be the discovery that the universe is infinitely old.
What did Richard Dawkins believe was difficult to prove?
---
Answer:
unanswerable