The following is a question from an Australian Mathematics Competition, and was to be done without using a calculator.
The two digit number ab (a and b are digits) is divisible by 7. If ba means the transpose of ab (for example, 31 is the transpose of 13), which of the following must also be divisible by 7?
(1)...5 X b + a (2)...3 X a + b (3)...ba + a
Note,..at least one of the above is correct.
Be sure to show all your working so as to substantiate your answer, and remember...no calculators....pen and paper ONLY!
Have fun,...
Ron.
The two digit number ab (a and b are digits) is divisible by 7. If ba means the transpose of ab (for example, 31 is the transpose of 13), which of the following must also be divisible by 7?
(1)...5 X b + a (2)...3 X a + b (3)...ba + a
Note,..at least one of the above is correct.
Be sure to show all your working so as to substantiate your answer, and remember...no calculators....pen and paper ONLY!
Have fun,...
Ron.