Chapter 9.7, Problem 1P

To determine

To express: the equation expressing the fact.

Answer to Problem 1P

The expression is $t+u=15$ .

Explanation of Solution

Given information:

The sum of the digits of a two −digit number is 15.

Formula used:

Digit problems are based on our decimal system of numeration.

Step1. The problem asks for the original number.

Step2. Let t = the tens digit of the original number.

Let u = the units digit of the original number.

Step3. Use the facts of the problem to write two equations.

Step4. Solve the equations.

Calculation:

Consider ,

Let t = the tens digit of the original number.

Let u = the units digit of the original number.

	Tens	Units	Value
Original number	t	u	$10t+u$

According to the question,

  $=t+u=15$

Hence, the expression is $t+u=15$ .