Can you guys fill in the blank and explain why

  1.188×10¹⁰ pounds of stone

Step-by-step explanation:

You apparently have ...

  (2.4×10⁶ stones)×(4.95×10³ lb/stone) = (2.4×4.95)×10⁶⁺³ lbs

  = 11.88×10⁹ lbs

  = 1.188×10¹⁰ lbs

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When I know the product of the mantissas will be more than 10, I like to make an adjustment to the exponents before doing the multiplication. Here, that could be ...

  total weight = (2.4×10⁶ stones)×(0.495×10⁴ lb/stone) = 1.188×10¹⁰

Of course, the applicable rule of exponents is ...

  (10^a)(10^b) = 10^(a+b)

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Moving the decimal point and adjusting the exponent accordingly should be no mystery. You want the value of the number to be the same, regardless of the form it is in.

  4.95 = 0.495×10

  11.88 = 1.188×10

Your calculator or spreadsheet will deal with numbers in scientific notation and will return their product in that format, if you choose.