Question

How far will a train travel in 5 hours if it travels at 80 miles per hour?

Answer 1

Answer:

  C.  400 miles

Step-by-step explanation:

In each hour, it travels 80 miles. (That is the meaning of "80 miles per hour.") So you can add up the distances over a period of 5 hours:

  80 miles + 80 miles + 80 miles + 80 miles + 80 miles

After the first sum (80+80=160), you can see what the correct answer will be. Continuing, you find the sum to be ...

  = 400 miles

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Multiplication was invented to make repeated addition easier.

  5 × 80 miles = 400 miles

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Strictly speaking, you are multiplying numbers with units here:

  (5 h) × (80 mi/h) = 400 mi·h/h = 400 mi . . . . . . the units h/h cancel