Given: 3780/18=
Sol.A: 18=2x3x3=2x9, so if 3780 is divisible by 18, 3780 would be divisible
by both 2 and 9 as well, because 2 and 9 are co-prime, don't share any
divisors other than 1.*
3780/2=1890 and 1890/9=210. That is: 3780/(2x9)=(3780/2)/9=1890/9=210
The answer is: 3780/18=210
Sol.B: Think simple multiple of 18 nearer to 3780.
18x2=36, so 18x200=3600 Thus, 3600/18=200
3780-3600=180, and 180/18=10 That is:
3780/18=(3600+180)/18=3600/18 + 180/18=200+10=210
The answer is: 3780/18=210
* The ones digit of 3780 is 0, so 3780 is divisible by 2. And the sum of each digit of 3780 is 18 (=3+7+8+0), so 3780 is divisible by 9