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Integer Digit Problem

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Integer Digit Problem

by wcheng57 » Fri Jun 04, 2010 9:54 pm
This was a real GMAT problem from an old GMAT Test Paper exam.

How many integers between 324,700 and 458,600 have tens digit 1 and units digit 3?

a) 10,300

b) 10,030

c) 1353

d) 1352

e) 1339


E is the correct answer. Could someone explain how one would do this problem in under 2 minutes? Thanks.
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by pradeepkaushal9518 » Fri Jun 04, 2010 10:06 pm
imo E is answer 1339

as 458600-324700=133900

in every 100 there is one no having 13 so 133900/100=1339

it takes me only 1 min
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by iikarthik » Fri Jun 04, 2010 11:55 pm
The unit disgit -3 repeats itself for every 10 consecutive nos
But the tenth digit -1 repeats itself only for every 100 consecutive nos.
We need both the 1 and 3 to be present for that number to get counted.
so the counting of 3 can be ignored it can't be counted without the presence of digit 1 that repeats once in 100 numbers.

so 458600-324700 = 133900

since the required combination repeats itself once in 100 numbers

133900/100, we get 1339
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