Seven Times

Author: Taio killick
4 years ago

Riddle: What is the smallest whole number that is equal to seven times the sum of its digits?
Answer: The answer to this math riddle is 21. You probably just guessed to answer this math riddle, which is fine, but you can also work it out algebraically. The two-digit number ab stands for 10a + b since the first digit represents 10s and the second represents units. If 10a + b = 7(a + b), then 10a + b = 7a + 7b, and so 3a = 6b, or, more simply, a = 2b. That is, the second digit must be twice the first. The smallest such number is 21.
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Source: https://www.riddles.com/9051
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What is the smallest whole number that is equal to seven times the sum of its digits?
Seven times by Taio killick v1.


Riddle: What is the smallest whole number that is equal to seven times the sum of its digits? Answer: The answer to this math riddle is 21. You probably just guessed to answer this <a href="/math-riddles">math riddle</a>, which is fine, but you can also work it out algebraically. The two-digit number ab stands for 10a + b since the first digit represents 10s and the second represents units. If 10a + b = 7(a + b), then 10a + b = 7a + 7b, and so 3a = 6b, or, more simply, a = 2b. That is, the second digit must be twice the first. The smallest such number is 21.
by Taio killick v2.