Remember that: "Platinum Gym charges a one-time registration fee of $60, and membership is $20 a month."
We are solving for a membership that will make Edward's statement untrue, that the gym membership fee will NOT have a month where the cost is the same.
For example, I can say that:
" Bob's Gym charges a one-time registration fee of $50, and membership is $10 a month ".
In this case, the pricing is much lower than Platinum Gym's and would not have a chance of getting the same cost in the same month.
Another example can be:
" SuperSneaker's charges a one-time registration fee of $100, and membership is $30. "
Again, the cost is much more higher than Platinum Gym's and would not have a chance of getting the same cost in the same month.
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hope this helps