I'll just do the one for 7. The others are done exactly the same way: To find the smallest 12 digit multiple of 7, Let the number to multiply 7 by to get a 12-digit number be n. Then 7n ≧ 100000000000 Divide both sides by 7 n ≧ 14285714285.714··· [if you need a calculator that shows that many digits, there is one online here: http://web2.0calc.com/ ] The smallest integer n that fits that is n = 14285714286 Answer: 7×14285714286 = 100000000002 Repeat the above procedures with 3,4,5, and 6 to get the others. Edwin