Is there a quick way of figuring out how many integers there are between 250 and 300, inclusive, that can be evenly divided by NEITHER 3 NOR 5?
Listing all the numbers are time consuming and not advisable for the GMAT.
Integers
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Number of total integers = 300 - 250 + 1 = 51
Total Divisible by 3 = (300 - 252)/3 = 16
Total Divisible by 5 = (300 - 250)/5 = 10
Total Divisible by both = 255, 270, 290
(first first one divisble by both and add 15 to each one)
16 + 10 - 3 = 23 ( are divisible by either)
51 - 23 = 28 (not divisible)
IMO 28
Looks long when you write it out, but only took me about 1 min to solve.
Total Divisible by 3 = (300 - 252)/3 = 16
Total Divisible by 5 = (300 - 250)/5 = 10
Total Divisible by both = 255, 270, 290
(first first one divisble by both and add 15 to each one)
16 + 10 - 3 = 23 ( are divisible by either)
51 - 23 = 28 (not divisible)
IMO 28
Looks long when you write it out, but only took me about 1 min to solve.
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Thanks for the short cut, but the book has an answer of 27. There are 11 integers divisible by 5 and 13 integers divisible by 3, for a total of 24.
51-24=27
51-24=27
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mike's method is Ok but his counting is wrong
total number of integers=51
total divisible by 3=(300-252)/3+1=17
total divisible by 5=(350-250)/5+1=11
divisible by both=(300-250)/15 (take the quotient)+1 i.e. 4 and the numbers are 255,270,285 and 300
17+11-4=24
so numbers not divisible=51-24=27
total number of integers=51
total divisible by 3=(300-252)/3+1=17
total divisible by 5=(350-250)/5+1=11
divisible by both=(300-250)/15 (take the quotient)+1 i.e. 4 and the numbers are 255,270,285 and 300
17+11-4=24
so numbers not divisible=51-24=27
The powers of two are bloody impolite!!