Question
How many different products can be obtained by multiplying two or more of the numbers 3, 5, 7, 11 (without repetition)?

Answer

The we can multiplying 2 or 3 or 4 digits. Then number of ways of multiplying 4 digits at a time $={^\text{4}}\text{C}_{4}\ ....(\text{i})$ Then number of ways of multiplying 4 digits at a time $={^\text{4}}\text{C}_{3}\ ....(\text{ii})$ Then number of ways of multiplying 4 digits at a time $={^\text{4}}\text{C}_{2}\ ....(\text{iii})$ Total number of ways $={^\text{4}}\text{C}_{4}+{^\text{4}}\text{C}_{2}+{^\text{4}}\text{C}_{3}$ $=1+\frac{4\times3}{2}+4$ $=11$

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