The number of permutations can be made of the letters of the word "radar" when taken all at a time is 30.
This is defined as ways in which n things can be arranged, taken all at a time.
P(n,r) = n!/(n-r)!
Radar has 5 words with 2r , 2a and 1d which means
5! / 2! 2! 1!
5! = 5×4×3×2×1 = 120
2! 2! 1! = 4
120/4 = 30
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