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| Place a digit from 0-9 into each of the 7 locations, such that each of the three numbers read from top-to-bottom in each of the three directions is divisible by 7. You can use a single digit more than once, but each of the 9 multi-digit numbers must be unique. (The numbers are the 2-digit numbers AC, AB, BE, CF, EG and FG, and the 3-digit numbers ADG, BDF and CDE.) To minimize variations, choose B < C, and E < F. |
A B C D E F G H I J |
| Place a digit from 0-9 into each of the 10 locations, such that all of the 2-digit multiples of 7 (except 77) can be found vertically, horizontally, or diagonally. There are a variety of solutions, so also try to arrange the numbers to produce as many 3-digit multiples of 7 as you can. To minimize variations, minimize higher locations first, then left locations. |
Source: 1. The Great Book of Mind Teasers & Mind Puzzlers, 1986, p. 177. 2. Original.