Cheryl had enough money to buy either 16 pens or 24 erasers.She spent all her money on these 2 items.
If she brought 12 pens, how many erasers did she buy?
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According to the condition, 16 pens cost the same amount as 24 erasers.
Hence, 4 pens cost the same amount as 6 erasers.
Cheryl bought 12 pens, hence the remainder of her money is equivalent to 4 pens, which in turn is equivalent to 6 erasers.
Answer. Cheryl bought 12 pens and 6 erasers.
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Be aware !: The solution by @gosgarithmetic is W R O N G and I N A D E Q U A T E !
He misread and misinterpreted the condition and the question of this simple problem.
As usual, @josgaritmetic solved the problem INCORRECTLY.
In future, when/if you get something from @josgarithmetic,
keep in mind that with 30% - 50% probability it is incorrect.
So do not hurry to accept his writing - with high probability it is WRONG.
@josgarithmetic, I proposed an agreement to you - and you demonstratively rejected, ignored and violated it.
You know what is I am talking about.
From now, I will attach this announcement written in bold above,
to each and every your incorrectly solved problem.
@josgarithmetic, GO AWAY from the forum.