Answer: 21
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Explanation:
x = the unknown number
x/3 = one third of the number
(x/3)+3 = added 3 to the previous result
(x/3)+3 = 10
x/3 = 10-3
x/3 = 7
x = 3*7
x = 21
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original number = 21
one third of it = 21/3 = 7
add on 3 to the previous result = 7+3 = 10
This confirms the answer.
