A
B
C
D
E
We have to get the unit digit of xy = 4^a*9^b; where a and b are positive integersBTGmoderatorDC wrote:If a and b are positive integers and x = 4^a and y = 9^b, which of the following is a possible units digit of xy?
a. 1
b. 4
c. 5
d. 7
e. 8
OA B
Source: Manhattan Prep
x is equal to a POWER OF 4:BTGmoderatorDC wrote:If a and b are positive integers and x = 4^a and y = 9^b, which of the following is a possible units digit of xy?
a. 1
b. 4
c. 5
d. 7
e. 8
Since x is even (notice that x is a power of 4) and y is odd (notice that y is a power of 9), then xy must be even and thus it has an even units digit. We can rule out choices A, C and D.BTGmoderatorDC wrote:If a and b are positive integers and x = 4^a and y = 9^b, which of the following is a possible units digit of xy?
a. 1
b. 4
c. 5
d. 7
e. 8
