"Divisible by" means that you can carry out the division, and that you'll get a whole number. Or, if you use whole number division, that there will be no remainder. For example: 8 divided by 2 = 4, remainder zero. 8 is divisible by 2. On the other hand, 9 divided by 2 = 4, remainder 1 (on a calculator, you get decimals: 4.5). That means that 9 is not divisible by 2.
15 of them are.
51 and 57
Yes
The divisibility rule for 3 is add up the digits and check for divisibility. 7+2+4 = 13.13 is not evenly divisible by 3 so 724 is not divisibleby 3.
9 x 12 = 108 9 x 13 = 117 9 x 14 = 126 9 x 15 = 135 9 x 16 = 144 9 x 17 = 153 9 x 18 = 162 9 x 19 = 171 ...... 9 x 55 = 495.
You would say to yourself:-- If it has to be divisible by 5 and 9, then it's divisible by 45.-- The biggest 3-digit number is 999.-- 999 divided by 45 is 22.2-- So if I multiply 45 by only 22 and leave off the 0.2,I'll get the biggest one that's less than 999.-- 45 x 22 = 990 .