12 plus two fifths of a number is 30. Find the number (by equation)

12 plus two fifths of a number is 30. Find the number (by equation)

Let this number be X
12+2/5x=30
2/5x=18
x=45
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A number 5.5 times is 31.25 more than 3 times. What's the number / use the inverse solution

Let the single digit be x and the ten digit be y
①2Y=X
②10Y+X+27=10X+Y
From ②, we get that ③ 27 = 9x-9y
Substitute ① into ③ to get 27 = 18y-9y
Y=3
Substituting (1)
X=6
So the original number is 36
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