Question 980962
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{{{K=kwh_used}}}; {{{M[L]=lowest_monthly_bill}}}; {{{M[H]=highest_monthly_bill}}}
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{{{(M[L]-20)/0.04}}}<{{{K}}}<{{{(M[H]-20)/0.04}}}
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{{{(60-20)/0.04}}}<{{{K}}}<{{{(80-20)/0.04}}}
.
{{{40/0.04}}}<{{{K}}}<{{{60/0.04}}}
.
{{{1000kwh}}}<{{{K}}}<{{{1500kwh}}}

ANSWER: The range of kwh used is between 1000kwh and 1500kwh.