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'Mini Kakuro' printed from http://nrich.maths.org/
From the second row we see that c, d, e are 1, 2, 4 in some order; and from the third column we see that e> 2. Hence e=4 and we may now deduce that g=8 and so f=5.
(Although their values are not required, it is now also possible to deduce that c=1, a=3, b=9, d=2.)
This problem is taken from the UKMT Mathematical Challenges.