Brain Teasers
3-digit Number
There's a 3-digit number. The sum of its digits is 10, the product of its digits is 20, and it is divisible by 7. What is the 3-digit number?
Answer
The 1-digit factors of 20 are 1, 2, 4 and 5, therefore, the number is made up of 1, 4 and 5.Out of the six numbers formed by the 3 digits, 145, 154, 415, 451, 514 and 541, only 154 is divisible by 7.
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Comments
Pretty good.
I got 451 pretty good teaser! Makes me feel smart
oops miss read the answer It didn't make me feel smart
isnt 541 divisible by 7?
its 154 because 451 isnt divisible by 7 when you divide 154 by 7 you get 22
easy, but fun!
too easy
@snappytom: 541 is not divisible by 7.
Easy shortcut for divisibility by 7:
Cut the last digit off from the rest of the number, and double that last digit.
Then subtract that doubled digit from the first part of the number.
541 Cut last digit off
54 | 1 Double last digit
54 | 2 Subtract doubled digit from first part
52 If this number is divisible by 7, then the original one is as well divisible by 7.
52 is not a multiple of 7; therefore, neither is 541.
154
15 | 4
15 | 4x2 = 8
15 - 8 = 7
7 is a multiple of 7, so 154 is divisible by seven.
Easy shortcut for divisibility by 7:
Cut the last digit off from the rest of the number, and double that last digit.
Then subtract that doubled digit from the first part of the number.
541 Cut last digit off
54 | 1 Double last digit
54 | 2 Subtract doubled digit from first part
52 If this number is divisible by 7, then the original one is as well divisible by 7.
52 is not a multiple of 7; therefore, neither is 541.
154
15 | 4
15 | 4x2 = 8
15 - 8 = 7
7 is a multiple of 7, so 154 is divisible by seven.
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