How many three digit numbers can be made up from the digits 1 to 5 if: a) no repetition is allowed and the number must be greater than 500? b) repetition is allowed and the number must be less than 300?.
For part a, I got 12, because 1*4*3 = 12, but the answer is 24.
Part b, the answer is 1250.
Please explain your answers.
2007-04-17 06:21:07 · 4 answers · asked by Anonymous in Science & Mathematics ➔ Mathematics
a. I agree with 12
b. 2*5*5 = 50
So I don't agree with the book answers.
2007-04-17 06:26:40 · answer #1 · answered by fcas80 7 · 0⤊ 0⤋
Not sur what no repetitions allowed means. Is 555 not allowed? Is 511 not allowed? Is 512 and 521 a repetition?If so, you first answer is correct.
The answer to the second question cannot possibly be 1250.
Only the numbers 111 through 255 are eligible. Regardless of repititions or not. The answer would seem to be 2*5*5=50.
Suggest you make sure you have stated problem and answers correctly.
2007-04-17 13:44:24 · answer #2 · answered by ironduke8159 7 · 0⤊ 0⤋
a)
The first place has to be taken by a 5.
this implies we have to fill 4 places with any of the four remaining nos.
NO. of cases : 4*3*2*1 = 24
b)
The first one cannot be a 3, 4, or 5
this implies options for place 1(10 thousands place) : 2
place 2(thousands place) : 5
place 3(hundreds place) : 5
place 4(tens) : 5
place 5(units) : 5
Total=5*5*5*5*2 = 1250
2007-04-17 13:35:55 · answer #3 · answered by Second Newton... 2 · 0⤊ 2⤋
good question but i dunno!
2007-04-17 13:27:09 · answer #4 · answered by greaterrome 2 · 0⤊ 0⤋