Problem: The Weston Cadet (model 852 introduced in 1949), Direct Reading (model 853 introduced 1954) and Master III (models 737 and S141.3 introduced in 1956) were the first in their line of exposure meters to switch and utilize the meanwhile established ASA scale instead. Other models used the original Weston scale up until ca. 1955. The company continued to publish Weston film ratings after 1955, but while their recommended values often differed slightly from the ASA film speeds found on film boxes, these newer Weston values were based on the ASA system and had to be converted for use with older Weston meters by subtracting 1/3 exposure stop as per Weston's recommendation. Vice versa, "old" Weston film speed ratings could be converted into "new" Westons and the ASA scale by adding the same amount, that is, a film rating of 100 Weston (up to 1955) corresponded with 125 ASA (as per ASA PH2.5-1954 and before). This conversion was not necessary on Weston meters manufactured and Weston film ratings published since 1956 due to their inherent use of the ASA system; however the changes of the ASA PH2.5-1960 revision may be taken into account when comparing with newer ASA or ISO values.
Beginning with which year was the Weston to ASA conversion not necessary?
The answer is the following: 1956

Problem: Madonna holds the record for the most number-ones on all combined Billboard charts, including twelve number-one songs on the Billboard Hot 100 and eight number-one albums on the Billboard 200. With 45 songs topping the Hot Dance Club Songs chart, Madonna became the artist with the most number-one songs on an active Billboard chart, pulling ahead of George Strait with 44 number-one songs on the Hot Country Songs chart. She has also scored 38 top-ten singles on the Hot 100, more than any other artist in history. In 2008, Billboard magazine ranked her at number two, behind The Beatles, on the Billboard Hot 100 All-Time Top Artists, making her the most successful solo artist in the history of American singles chart.
Who has the most number one songs in an active BiIlboard chart?
The answer is the following: Madonna

Problem: Mechanical pulping yields almost a tonne of pulp per tonne of dry wood used, which is why mechanical pulps are sometimes referred to as "high yield" pulps. With almost twice the yield as chemical pulping, mechanical pulps is often cheaper. Mass-market paperback books and newspapers tend to use mechanical papers. Book publishers tend to use acid-free paper, made from fully bleached chemical pulps for hardback and trade paperback books.
What level of acid is usually found in the paper used by book publishers?
The answer is the following: acid-free

Problem: In 1207, the Mongol ruler Genghis Khan (r. 12061227) conquered and subjugated the ethnic Tangut state of the Western Xia (10381227). In the same year, he established diplomatic relations with Tibet by sending envoys there. The conquest of the Western Xia alarmed Tibetan rulers, who decided to pay tribute to the Mongols. However, when they ceased to pay tribute after Genghis Khan's death, his successor Ogedei Khan (r. 12291241) launched an invasion into Tibet.
Who invaded Tibet?
The answer is the following:
Ogedei Khan