1998 CEMC Gauss (Grade 8) Problems/Problem 1

Problem

The number $4567$ is tripled. The ones digit (units digit) in the resulting number is

$\text{ (A) }\ 5 \qquad\text{ (B) }\ 6 \qquad\text{ (C) }\ 7 \qquad\text{ (D) }\ 3 \qquad\text{ (E) }\ 1$

Solution 1

Tripling a number means that we are multiplying the number by $3$ .

We can multiply $4567 \times 3$ to get $13701$ . The units digit is therefore $\boxed {\textbf {(E) } 1}$

~anabel.disher

Solution 2

We can notice that only the units digit of $4567$ matters here, as $4000 \times 3$ , $500 \times 3$ , and $60 \times 3$ all have units digits of $0$ .

Therefore, the units digit would be the units digit of $7 \times 3$ = $21$ , which is $\boxed {\textbf {(E) } 1}$ .

~anabel.disher

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1998 CEMC Gauss (Grade 8) Problems/Problem 1

Problem

Solution 1

Solution 2