Mykola V. answered 01/11/13
Math Tutor - Patient and Experienced
We only have multiplication and division to work with. So the way to approach this problem is to find all factors of 99 and a few multiples of it as well.
Factors: 1, 3, 9, 11, 33, 99. The only ones we can use are 3, 33 because we can't use the 9 key.
Multiples of 99: 99, 198, 297, 396, 495, 594, 693, 792, 891, 990, 1089, 1188, 1287, 1386, 1485, 1584... We can't use any multiple with 9 in it but the rest seem good.
So we can already construct all of the solutions starting with the factors 3, 33:
1. 3 × 33 = 99
Now we use division and the multiples:
2. 1188 ÷ 12 = 99
3. 1287 ÷ 13 = 99
4. 1386 ÷ 14 = 99
5. 1485 ÷ 15 = 99
Of course there are more solutions because we can keep going up in multiples without using 9's. Hope this helped!