Problems based on Numbers Test 5

Concept:The unit digit of a product depends only on the unit digits of its factors.Explanation:Powers of $3$ repeat their unit digits every $4$ terms: $3, 9, 7, 1$.For $3^{28}$, $28 \div 4$ leaves remainder $0$, so the unit digit is $1$.Powers of $11$ always end in $1$, so $11^{42}$ has unit digit $1$.Powers of $7$ repeat their unit digits every $4$ terms: $7, 9, 3, 1$.For $7^{35}$, $35 \div 4$ leaves remainder $3$, so the unit digit is $3$.Now multiply the unit digits: $1 \times 1 \times 3 = 3$.Answer:The unit digit is $3$, which matches option B.