Thursday, September 17, 2026

These are the 10 questions BrainRank served to the whole world on Thursday, September 17, 2026 — now over, with every answer revealed and explained. Reading time only; the score no longer counts.

1. history

   Which ancient empire was founded by Cyrus the Great and centered in what is now Iran?

   • Greek Empire
   • Roman Empire
   • Persian Empire
   • Egyptian Empire

   Answer: Persian Empire

   The Persian (Achaemenid) Empire was founded by Cyrus the Great and centered in modern Iran.

2. mythology

   In Roman mythology, which two-faced god of doorways and beginnings gives January its name?

   • Bacchus
   • Neptune
   • Pluto
   • Janus

   Answer: Janus

   Janus, shown with two faces looking forward and back, is the namesake of January.

3. science

   Which chemical symbol represents the element calcium?

   • Cl
   • Cm
   • Cc
   • Ca

   Answer: Ca

   Ca is the chemical symbol for calcium.

4. geography

   Lake Baikal, the world's deepest freshwater lake, is located in which country?

   • Mongolia
   • Kazakhstan
   • China
   • Russia

   Answer: Russia

   Lake Baikal is in southern Siberia, Russia.

5. mythology

   In Greek mythology, the Hydra was a monster known for which ability?

   • Turning onlookers to stone
   • Growing back heads that were cut off
   • Flying faster than an arrow
   • Changing shape at will

   Answer: Growing back heads that were cut off

   The Lernaean Hydra regrew heads whenever one was cut off, which is why Heracles seared the stumps.

6. nature

   Which cell structure is often called the powerhouse of the cell?

   • Nucleus
   • Ribosome
   • Vacuole
   • Mitochondria

   Answer: Mitochondria

   Mitochondria generate most of the cell's energy (ATP).

7. everyday-science

   Which instrument is used to measure atmospheric pressure for weather forecasting?

   • Barometer
   • Thermometer
   • Anemometer
   • Hygrometer

   Answer: Barometer

   A barometer measures atmospheric pressure, useful in weather prediction.

8. history

   Which civilization built the ancient city of Machu Picchu in the Andes?

   • Aztecs
   • Maya
   • Olmecs
   • Inca

   Answer: Inca

   Machu Picchu was built by the Inca civilization in the Andes of Peru.

9. math

   What is 50% of 90?

   • 40
   • 45
   • 50
   • 35

   Answer: 45

   50% of 90 = 45.

10. geography

    The Great Barrier Reef lies off the coast of which country?

    • Indonesia
    • Philippines
    • Australia
    • New Zealand

    Answer: Australia

    The Great Barrier Reef is off the northeastern coast of Australia.