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Study homework help
by Dagmara_4871 Leaving Cert Mathematics — 13/09/16 3

This maths question is really bugging me. In my Active Maths Book 1 pg 116 question 13, there is a question on palindromic numbers. I understand the term palindromic and got my first answer to part (i) which asked me the amount of 3 digit palindromic number ...my answer is 90 ...now it asks me to find the number of palindromic numbers between 10 to the power of 6 and 10 to the power of 7. I know from the back of the book that the answer is supposed to be 9000 but when i try the question i get a different answer. Andyone know how to do it?


3 Comments
michaels — 31/08/16
(i) 9x10x1 = 90 (ii)10^6 = 1000000 10^7 = 10000000 therefore 9 x 10 x 10 x 10 x 1 x 1 x 1 = 9000
michaels — 31/08/16
Hope that helps
smcshane — 13/09/16
Michaels is correct, 10^6 is a seven digit number and 10^7 is an eight digit number so all the numbers in between are 7 digit numbers. 9 choices (1-9) for the first digit, which means 1 for the seventh (as it has to be the same) 10 choices (0-9) for the second digit, which means 1 for the sixth (as it as to be the same) 10 choices (0-9) for the third digit, which means 1 for the fifth (as it as to be the same) 10 choices (0-9) for the fourth digit. So thats where you get 9 x 10 x 10 x 10 x 1 x 1 x 1 = 9,000
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