Question

a man leaves 1/2 of his property for his wife and1/5 of it for his daughter and the rest for his son.How much did his son get ?

Answer 1

1/2+1/5 = 5+2/10 ...lcm
1-7/10 = property for son
10-7/10 =3/10 his son got 3/10th part of property

Answer 2

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total = 1
wife share=1/2
daughter share =1/5
Therefore,
Son share = 1 -1/2 -1/5
=3/10
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by @strange