Total number of girls = 40

1. 30 of them play hockey - No information about girls who play football. Insuff.

2. 10 of them play football - No information about girls who play hockey. Insuff.

Both 1 & 2 together,

Case 1:

It is possible that the 10 girls who play football can also play hockey. In that case the answer will be 10;

Case 2:

It is possible that 30 girls play only hockey ad remaining 10 girls play only football. In that case the answer will be 0;

Hence, Insuff.

Ans: E.

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