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Linear inequalities in one or two variables SAT question
Math · Algebra · Hard · Answer it here, explanation included.
The formula above is Ohm’s law for an electric circuit with current I, in amperes, potential difference V, in volts, and resistance R, in ohms. A circuit has a resistance of 500 ohms, and its potential difference will be generated by n six-volt batteries that produce a total potential difference of 
volts. If the circuit is to have a current of no more than 0.25 ampere, what is the greatest number, n, of six-volt batteries that can be used?
Enter a number or fraction (like 3/17 or 0.176). Press Enter to check.
ExplanationShow
The correct answer is 20. For the given circuit, the resistance R is 500 ohms, and the total potential difference V generated by n batteries is volts. It’s also given that the circuit is to have a current of no more than 0.25 ampere, which can be expressed as 
. Since Ohm’s law says that , the given values for V and R can be substituted for I in this inequality, which yields 
. Multiplying both sides of this inequality by 500 yields 
, and dividing both sides of this inequality by 6 yields 
. Since the number of batteries must be a whole number less than 20.833, the greatest number of batteries that can be used in this circuit is 20.
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