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The sum of two whole number is 45 and their difference is less than 10. The number of all possible pairs is
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x + y = 45, (1)
x - y < 10. (2) (where x is the larger number)
Express x from (1): x = 45 - y, and substitute it into (2). You will get
45 - y - y < 10, or
45 - 2y < 10, or
2y > 45 - 10, or
y > (45 - 10)/2.
Hence, y > 17. Then x < 10 + 17 = 27. (And x > y).
Answer. These 5 pairs (27,18), (26,19), (25,20), (24,21), (23,22)
and 5 reversed pairs (18,27), (19,26), (20,25), (21,24), (22,23) is the full list of solutions.
In all, there are 10 different pairs of solutions, listed above.