Bunuel wrote:
The integer P is greater than 7. If the integer P leaves a remainder of 4 when divided by 9, all of the following must be true EXCEPT
A. The number that is 4 less than P is a multiple of 9.
B. The number that is 5 more than P is a multiple of 9.
C. The number that is 2 more than P is a multiple of 3.
D. When divided by 3, P will leave a remainder of 1.
E. When divided by 2, P will leave remainder of 1.
We can create the following equation:
P = 9Q + 4
Thus, we see that P can be values such as:
13, 22, 31, 40, ...
Let’s review the answer choices.
A) The number that is 4 less than P is a multiple of 9.
P - 4 = 9Q + 4 - 4
P - 4 = 9Q
A is true.
B) The number that is 5 more than P is a multiple of 9.
P + 5 = 9Q + 4 + 5
P + 5 = 9Q + 9
B is true.
C) The number that is 2 more than P is a multiple of 3.
P + 2 = 9Q + 4 + 2
P + 2 = 9Q + 6
C is true.
D) When divided by 3, P will leave a remainder of 1.
(9Q + 4)/3 = (3Q + 1) + 1/3
D is true.
E) When divided by 2, P will leave remainder of 1.
(9Q + 2)/2 = (4Q + 1) + Q/2
We can’t be certain what the remainder is. If Q = 1, then the remainder is 1; however, if Q is 2, then the remainder is 0.
Alternate solution:
Since the problem says all of the answer choices must be true except one of them, we can use any integer > 7 that satisfies the condition “when it is divided by 9, it will leave a remainder of 4” to check the answer choices. Since 13 is one such number, we will use that.
A) 13 - 4 = 9 and 9 is a multiple of 9. This is true.
B) 13 + 5 = 18 and 18 is a multiple of 9. This is true.
C) 13 + 2 = 15 and 15 is a multiple of 3. This is true.
D) 13/3 = 4 R 1. This is true.
E) 13/2 = 6 R 1. This is true.
Since 13 makes all answer choices true, we need to use another number. Another number we can use is 13 + 9 = 22.
Instead of checking each answer choice again, we can see that choice E is not true, since when 22 is divided by 2, the remainder is 0, not 1.
Answer: E