Recall: distance = rate times time.
To determine how far apart the two cars will be after four hours of travel, subtract the sum of the distances traveled from 200 mi:
Distance apart after four hours = 200 mi - (40 mph)(4 hrs) - (35 mph)(4 hrs)
= 200 mi - 160 mi - 140 mi = -100 mi
The wording of your question implies that the cars will not yet have met after four hours of travel. This negative result is absurd. Please ensure that you have copied down the problem completely and accurately.
The "rule of 72" says that the doubling time in years is approximately 72 divided by the interest rate in percent. To make the money grow by a factor of 4 requires that it double twice, so will take twice as long as the period to double once.
2×72/11.3 ≈ 12.7 . . . . years
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The "rule of 72" is an approximation. The actual quadrupling time for this interest rate and compounding is about 12.6 years. (The actual product of doubling time and nominal interest rate is about 71.25.)
We can use prime factorization to find the GCF:
The greatest value both 12 and 20 share is 4. By factoring this out of the equation, we get:
4(3 + 5) = 4(8) = 32
