A) 1260
B) 2500
C) 625
D) 500
Correct Answer: A
Solution :
[a]\[{{6}^{a}}+{{9}^{b}}={{(5+1)}^{a}}+{{(10-1)}^{b}}\] |
\[=5\lambda +(1){}^\circ +10\mu +{{(-1)}^{b}}\] |
\[=5\,(\lambda +24)+{{(1)}^{a}}+{{(-1)}^{b}}\] |
is divisible by 5 if b is odd. |
\[\therefore \] Total number of ordered pair \[(a,b)\] |
\[=50\times 25=1250\] |
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