How many permutations exist of the letters a, b,c, d taken three at a time? a.24 b.12 c.4

4P3 = 24
In a permutation order matters.
You can also think about it in this way; you have 3 spots to fill,
the first spot you have 4 items to choose from. Now there are only 3 items left to choose for the next spot. There are only 2 items left for the third spot, so
4 * 3 * 2 = 24
Letter A

It's like discovering the answer to a puzzle. the purpose in solving an equation is to find the value or values of the variable that makes it a true statement. any value of the variable that makes the equation true is called a solution to the equation.