Answer: 21.
Explanation:
Sally=x, Sam=y
x=3y
x+y=28
Substitution works. Since we know x is 3y, we can substitute the x in the second equation for 3y.
3y+y=28 ---> 4y=28
Divide both sides by 4 and y=7. You can plug in y to either equation, but the first one seems easier.
x=3(7)
x=21
Answer: 21 Erasers
Let x be the number of pencil erasers that Sam has.
Sally has 3x pencil erasers.
Together, they have x + 3x = 28 erasers.
4x = 28
x = 7 erasers.
Sally has 3 * 7 = 21 erasers.
So the answer is 21
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