Answer:
All the ordered pairs (a,b) are
(0,5), (2,3), (4,1), (6,8), and (8,6).
Explanation:
765ab4 to be divisible by 36, it must be divisible by both 9 and 4.
For any number to be divisible by 4, the last two digits of the number must be divisible by 4.
Here, the last two digits are b4, so as the number b4 is divisible by 4, b can be 0,2,4,6, and 8.
For any number to be divisible by 9, the sum of all the digit of the number must be divisible by 9.
Here, the sum of all the digits, S= 7+6+5+a+b+4=22+a+b.
Now, we have b={0,2,4,6, 8}
For b=0,
S=22+a+0=22+a which is a multiple of 9.
So, the possible value of the digit a :
a=5
So, (a,b)=(0,5)
For b=2,
S=22+a+2=24+a which is a multiple of 9.
So, the possible value of the digit a :
a=3
So, (a,b)=(2,3)
For b=4,
S=22+a+4=26+a which is a multiple of 9.
So, the possible value of the digit a :
a=1
So, (a,b)=(4,1)
For b=6,
S=22+a+6=28+a which is a multiple of 9.
So, the possible value of the digit a :
a=8
So, (a,b)=(6,8)
For b=8,
S=22+a+8=30+a which is a multiple of 9.
So, the possible value of the digit a :
a=6
So, (a,b)=(8,6)
Hence, all the ordered pairs (a,b) are
(0,5), (2,3), (4,1), (6,8), and (8,6).