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rxs0005
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Formula for finding multiples 23 Jul 2010, 06:43
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hi

is there a formula for finding evenly spaced numbers between 2 numbers

Eg

how many integers are there between 600 1999 inclusive that is divisible both by 13 and 5



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dauntingmcgee
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Formula for finding multiples 23 Jul 2010, 07:36
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I would think round down (1999-600)/(13*5) = 21
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azule45
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Formula for finding multiples 23 Jul 2010, 07:52
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I'll go with 20.

since we want to find divisibility by 13 AND 5, we need to look for the LCM of both values. 13*5 = 65. so we now want to find how many integers are divisible by 65.
we need find the lowest and highest divisibility values between 600 and 1999 inclusive. the highest is 1950 and the lowest is 650. therefore...

(1950 - 650) + 1 / 65 = 20 numbers.

did you have an OA?
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Formula for finding multiples 23 Jul 2010, 08:12
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azule45
I'll go with 20.

since we want to find divisibility by 13 AND 5, we need to look for the LCM of both values. 13*5 = 65. so we now want to find how many integers are divisible by 65.
we need find the lowest and highest divisibility values between 600 and 1999 inclusive. the highest is 1950 and the lowest is 650. therefore...

(1950 - 650) + 1 / 65 = 20 numbers.

did you have an OA?
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You are almost correct, except that your +1 should be after the fraction and not in the numerator to get (1950-650)/65 + 1. If you calculate it this way you will also get 21.

In your solution you must +1 because you are starting and ending on the multiples, while in mine I am not. Given the numbers involved, I recognized that we were not both starting and ending on a multiple so all that was necessary was to divide the range by LCM and round down.



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