A) 1
B) 2
C) 5
D) 7
Correct Answer: D
Solution :
\[{{7}^{1}}=7,\]\[{{7}^{2}}=49,\]\[{{7}^{3}}=343,\]\[{{7}^{4}}=2401,\]\[{{7}^{5}}=16807\] i.e., The unit's digit repeats itself after power 4. Remainder after we divide 245 by 4 =1 \[\therefore \] Unit's digit in the product of \[{{(4387)}^{245}}\times {{(621)}^{72}}=\]Unit's digit in the product of \[{{(4387)}^{1}}\times {{(621)}^{72}}=7\times 1=7\]
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