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If we place a 3 at both ends of an number, its value is increased by 3372.
Find the original number.
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Let the original integer number be x.
It is almost obvious (and easy to show) that the original number is a two-digit number.
If we place a 3 at both ends of such a number, its value becomes 3000+10x+3.
Therefore, according to the condition, we should find x from this equation
(3000 + 10x + 3) - x = 3372.
It is easy
10x - x = 3372 - 3000 - 3
9x = 369
x = 369/9 = 41.
CHECK. 3413 - 41 = 3372, the increase value. ! correct !
ANSWER. The original number is 41.