Bunuel wrote:
Which of the following is the lowest positive integer that is divisible by 2, 3, 4, 5, 6, 7, 8, and 9?
A. 15,120
B. 3,024
C. 2,520
D. 1,890
E. 1,680
Since we have to check the numbers for the divisibility by 2, 3, 4, 5, 6, 7, 8, 9 ... We just need to check the divisibility by 5,7,8,9
So we will start checking the options one by one for the divisibility by 5,7,8, 9.
To solve the problem in a faster way, we need to go through options very smartly and hence recheck the question. (I solved the question in 2:40 seconds which is on the higher side because I checked the divisibility of each number by 5,7,8,9 and there were 2 numbers divisible by all then I noticed that the question is asking for lowest positive integer.)
So how to solve this problem in smartly and in timely manner.
what to keep in mind.
1. As the question says we need to find the lowest positive integer divisible. So we should start from the lowest integer in the options.
2. We need to start from the number for which divisibility check is easier e.g. 5
Shortest way : Since this question ask for the lowest positive integer divisible by numbers .
This is the LCM of numbers 5x7x8x9 = 2520 Answer C.
Shorter way : If the question would have asked for lowest positive integer from the options.
Then,
1st check 1680 : Divisible by 5, Divisible by 8 , But not divisible by 9. No need to check divisibility by 7.
2nd 1890 : Divisible by 5, Not divisible by 8. No need to check divisibility by 9 and 7
3rd 2520 : Divisible by 5, divisible by 8, divisible by 9 , divisible by 7
So C is the correct option.
Finally don't forget to give kudos..