Tens Digit Twice the Ones Digit

Probability Level 1

Arpit is thinking of a 2-digit number whose tens digit is equal to twice the ones digit. How many different numbers can Arpit be thinking of?

Details and assumptions

The number $12 = 012$ is a two digit number, not a three digit number.

The answer is 4.

1 solution

Arron Kau Staff
May 13, 2014

Solution 1

If the ones digit is $a$ and the tens digit is $2a$ , then the number is $21 \times a$ . For this to be $2$ digits, the only possibilities are $21, 42, 63, 84$ . Therefore, Arpit could be thinking of 4 different numbers.

Solution 2

The tens digit has to be even, so it could be, 2, 4, 6, or 8. This gives $21, 42, 63, 84$ as the possible numbers. Therefore, Arpit could be thinking of 4 different numbers.

Tens Digit Twice the Ones Digit

The answer is 4.

1 solution

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