Units digit: Concept Units digit: Exercise 1. Find the units digit of $23 \times 47 \times 84$ a. 4 b. 6 c. 8 d. 0 Answer: A Explana...
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Units digit: Concept Units digit: Exercise 1. Find the units digit of $23 \times 47 \times 84$ a. 4 b. 6 c. 8 d. 0 Answer: A Explanation: We have to consider only units digits. $2\boxed3 \times 4\boxed7 \times 8\boxed4$ $ \Rightarrow 3 \times 7 \times 4$ $ \Rightarrow 2\boxed1 \times 4$ ($\because$ consider only units digit of any product.) $ \Rightarrow 1 \times 4 = 4$ Show Explanation Show Answer 2. Find the units digit of ${2^4} + {4^2} + {5^6} + {6^5}$ a. 2 b. 4 c. 6 d. 8 Answer: A Explanation: ${2^4} + {4^2} + 5 + 6$ $= 16 + 16 + 5 + 6 = \boxed3$ ($\because$ any power of 5 or 6 gives same units digit.) Show Explanation Show Answer 3. Find the units digit of $3^{20}$ a. 1 b. 3 c. 9 d. 7 Answer: A Explanation: As cyclicity for 3 is 4, we have to divide the power by 4. $\begin{array}{rl} 3^{20} &= {\left( {{3^4}} \right)^5} \\[4px] & = {\left( 1 \right)^5} \\[4px] & = 1 \end{array}$ Show Explanation Show Answer 4. ...