DMD to Be

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Albert does laundry once a week on Wednesdays and jogs on all even-numbered days. If he cleans his apartment every 5 days, and it was last cleaned Tuesday, March 1, how many days after this date will he do all three activities on the same day?

A. 8
B. 15
C. 16
D. 50
E. 51


If X is an even number and X + Y is an odd number, and X + Y + Z is an even number, which of the following could not describe YZ?

A. a multiple of Y-2
B. a multiple of X
C. a multiple of X/2
D. a multiple of X/4
E. a multiple of Z+4


How many three digit numbers containing no digits other than 2, 3, or 4 are divisible by 3?

A. 2
B. 3
C. 4
D. 6
E. 9
 

lintydent

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#1) I can't find an easier mathematical way, but i don't think it would be too time consuming to just draw SMTWThFS..draw an L under all the Wed. Tues is March 1st, so starting on Wed March 2nd, on every other day (which is an even number) write the letter J for jog, and then count every five days from March 1st Tues ...draw a C for clean and you get March 16th Wed.

Ans C

#3) There is the trick to know a number is divisible by 3 if all the digits in that number add up to a multiple of 3.

ie 222...2+2+2 = 6 and 6 is divisible by 3 so 222 is divisible by three.
Since you only have 3 digits you can play with and all three numbers 234 ... 2+3+4 add up to 9 which is divisible by 3 then any combination of 234 will work. How do you find the # of combinations? Factorials: 3x2x1= 6 possible combinations of 2 3 4 digit numbers. And then you can do 222, 333, and 444. So that's 9 ways.

Ans E
 
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DMD to Be

DMD to Be

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lintydent said:
#1) I can't find an easier mathematical way, but i don't think it would be too time consuming to just draw SMTWThFS..draw an L under all the Wed. Tues is March 1st, so starting on Wed March 2nd, on every other day (which is an even number) write the letter J for jog, and then count every five days from March 1st Tues ...draw a C for clean and you get March 16th Wed.

Ans C

#3) There is the trick to know a number is divisible by 3 if all the digits in that number add up to a multiple of 3.

ie 222...2+2+2 = 6 and 6 is divisible by 3 so 222 is divisible by three.
Since you only have 3 digits you can play with and all three numbers 234 ... 2+3+4 add up to 9 which is divisible by 3 then any combination of 234 will work. How do you find the # of combinations? Factorials: 3x2x1= 6 possible combinations of 2 3 4 digit numbers. And then you can do 222, 333, and 444. So that's 9 ways.

Ans E

How did you know to use 3x2x1?
 
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lintydent

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DMD to Be said:
How did you know to use 3x2x1?

Whenever you want to know how many possible combinations there are given n numbers, you apply the factorial rule.

So for example you have 4 different numbers, and you want to know the possible different combinations of rearranging the 4 different numbers you do 4x3x2x1= 24.

Try writing out the possibly combinations and then you'll see that it's the same thing as taking the factorial of the amount of numbers..or people..or whatever it is they give you. In that problem they give you three digits...so take factorial of three.
 
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DMD to Be

DMD to Be

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lintydent said:
Whenever you want to know how many possible combinations there are given n numbers, you apply the factorial rule.

So for example you have 4 different numbers, and you want to know the possible different combinations of rearranging the 4 different numbers you do 4x3x2x1= 24.

Try writing out the possibly combinations and then you'll see that it's the same thing as taking the factorial of the amount of numbers..or people..or whatever it is they give you. In that problem they give you three digits...so take factorial of three.

I see, thanks so much!! Oh, and the answer for #1 is supposedly B. ??
 

lintydent

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DMD to Be said:
I see, thanks so much!! Oh, and the answer for #1 is supposedly B. ??
He will do all three on Wed March 16th which is 15 days after the 1st. Tricky.
 
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