A combination lock has 20 numbers. To open the lock, rotate clockwise to the first number, counter-clockwise past the first number to the second number and then clockwise to the third number. How many different combinations are there if you CANNOT repeat a number in the combination
my work:
so first you have 3 spaces _ _ _ second, you have a combination lock of 20 numbers so first space is 20,second is 19,third is 18,so
20x19x18=6840
the answer is 6840
Is this the correct way of solving this problem?