There are 6 winning funds that grew more than 10%, and 4 losing funds that grew less than 10%.

The problem can be split into 3 sub-problems:

1) Sam has to choose 3 winning funds. This can be done in $6C_3$ ways.

2) Sam has to choose 1 losing fund. This can be done in $4C_1$ ways.

3) Sam has to choose all 4 funds to be winning funds. This can be done in $6C_4$ ways.

This is how Sam chooses at least 3 winning funds. Hence, the total number of ways of choosing at least 3 winning funds is $6C_3$*$4C_1$ + $6C_4$

If there were no restrictions (such as choosing at least 3 winning funds), Sam would have chosen funds in $10C_4$ ways.

Hence, the probability that at least 3 of Sam’s 4 funds grew by at least 10% over the last year is $\frac{6C_3*4C_1 + 6C_4}{10C_4}$

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