Question

Number of all five digit numbers of the form “34a5b”(where a, b are digits) divisible by 36, is___

Answer 1

x = 34a5b is divisible by 36
$\Rightarrow$34a 5b is divisible by 4 and 9.
Divisible by 4 : 5b is divisible by 4
$\Rightarrow b=2,6$
If b = 2 : 3 + 4 + a + 5 + 2 = 14 + a;
x is divisible by 9 $\Rightarrow$ a = 4
b = 6 : 3 + 4 + a + 5 + 6 = 18 + a
x is divisible 9 $\Rightarrow$ a = 0,9