17
There are 32C3 = 32*31*30/(3*2*1) = 4960 combinations. I do not have the inclination to list them all.
There is only one number that is equal to 15, and that is 15.
Four examples of irrational numbers are 21/2, 31/2, 51/2 & 71/3
There are no two real numbers that will add to -9 and multiply to 81. Using complex numbers, the two numbers are: (-9/2 + i9/2√3) and (-9/2 - i9/2√3)
31 and 3
31 = 1 + 2 + 3 + 4 + 21
30 1/3 31 1/3 32 1/3
They are: 7+11+13 = 31
Multiplied, 31 and 3 Divided, 279 and 3 Added, 90 and 3 Subtracted, 96 and 3
31 and 2
If by "equal up" you mean add up, there are at least two answers: (3, 7, 13, 31) and (5, 7, 11, 31).
13+7+6+5=31
The factors of 279 are: 1 3 9 31 93 279These pairs of numbers, when multiplied, equal 279:(1, 279)(3, 93)(9, 31)
31 and 2
1 x 279, 3 x 93, 9 x 31
3 and 31