Each piece of rope will be 7 meters
The empirical rule states that at 95% the measurements would be within 2 standard deviations of the mean.
You are given a mean of 68 inches and a standard deviation of 4.
2 times the standard deviation = 2 x 4 = 8
So 95% of the heights would be between 68-8 = 60 inches and 68+8 = 76 inches.
I think the answer is 378. Check to make sure!
For estimating purposes, you generally like to work with 1 significant digit, sometimes 2. The idea is to get a number "in the ballpark", sometimes along with an idea of whether that number is too high or too low. (The error estimate, too, is often approximated by 1 significant digit.)
22.8 × 4.7 ≈ 20 × 5 = 100
If you wanted a slightly more satisfying estimate, you could use
.. 23 × 5 = 115
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The actual value 4.7 is 0.3/5 = 6% lower than the value we're using in our computation. The actual value 22.8 = 2.8/10 = 14% higher than the value we're using for estimating. Hence the estimate of 100 may be 14%-6% = 8% lower than the actual value. (You can only add percentages like this when they are "small", so even this error estimate is in error.) That is, you exepect the actual value to be nearer 108. (22.8×4.7 is actually 107.16)
