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Which expression is equivalent to the expression shown?

The sum of the reciprocal of a positive number and the reciprocal of 2 more than the number is 3/4 equation: the number is

The brain volumes (cm cubed) of 50 brains vary from a low of 904 cm cubed to a high of 1488 cm cubed. use the range rule of thumb to estimate the standard deviation s and compare the result to the exact standard deviation of 175.5 cm cubed, assuming the estimate is accurate if it is within 15 cm cubed