VeritasPrepKarishma wrote:
sm021984 wrote:
What is the units digit of z if (385a)(225b) = z, where a and b are positive integers?
1) a = 3
2) a + b = 11
The unit's digit of z will be decided by the units digit of the two numbers.
Statement 1: a = 3
(3853)(225b) = z
Depending on what b is, the unit's digit of z can take different values.
If b = 1, unit's digit of z is 3.
If b = 2, unit's digit of z is 6.
etc
Not sufficient
Statement 2: a + b = 11
Again, there are many possible cases:
a = 2, b = 9, unit's digit of z is 8.
a = 3, b = 8, unit's digit of z is 4.
etc
Taking both together, we know a = 3 and b = 8. So unit's digit of z must be 4.
An interesting variation of this question could be:
What is the units digit of z if (385*a)(225*b) = z, where a and b are positive integers?
1) a = 3
2) a + b = 11
Try this one.
What is the units digit of z if (385*a)(225*b) = z, where a and b are positive integers?
1) a = 3
2) a + b = 11
-->
This should be B right.
My Explanation(ME not OE
)
385*a = last digit is 5 if a = odd, 0 if a = even
225*b = last digit is 5 if b = odd, 0 if b = even
1) Tells me a = odd, but nothing about b
So b =odd/even ==> Last digit = 0/5
Not sufficient
2) a+b=11 ==> one will be odd and the other even because 11 is odd
sum of an (odd and even)/(odd and odd) only gives an odd number
So answer will be 0 in all cases
So Sufficient
My Answer(MA should be OA
):
B