Question

Isaac drove at an average speed of 49 mph over 6 hours during the first three hours he drove at a speed that was 172 mph less than four times the speed he averaged for the last three hours how fast did he drive during the first 3 hours

Answer 1

Isaac drove the car at 44 mph during last three hours.

Step-by-step explanation:

Average speed = 49 miles per hour

Let,

s be the speed during last three hours

4s-172 be the speed during first three hours

Average = $\frac{Sum\ of\ items}{No.\ of\ items}$

$49=\frac{4s-172+s}{2}\\\\49*2=5s-172\\\\98=5s-172\\\\98+172=5s\\\\270=5s\\\\5s=270$

Dividing both sides by 5

$\frac{5s}{5}=\frac{270}{5}\\\\s=54$

Speed during last three hours = 54 mph

Speed during first three hours = 4(54)-172 = 44 mph

Isaac drove the car at 44 mph during last three hours.

Keywords: division, addition

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