Chapter 10, Problem 3CR

a.

To determine

To calculate the number of black cars

Answer to Problem 3CR

There are 21 black cars.

Explanation of Solution

Given information:

The total number of cars are 24.

There are 7 times as many as black cars as red cars.

Formula used: equation solving

Calculation:

Let, the number of red cars be x .

Therefore, the number of black cars are 7x

Since, there are 24 cars,

  $x+7x=24$

On solving,

  $8x=24$

Cross-multiplying both sides,

  $x=\frac{24}{8}$

On solving,

  $x=3$

Hence, number of red cars are 3.

For black cars, substituting the value of x

  $=7\times 3$

On solving,

  $=21$

Hence, number of black cars are 21

b.

To determine

To evaluate the mathematic practice used.

Answer to Problem 3CR

Equation making and solving is the practice used.

Explanation of Solution

Given information:

The total number of cars are 24.

There are 7 times as many as black cars as red cars.

Formula used:

Equation evaluation

Calculation:

Equation is made to solve the given problem. A statement that the values of two mathematical expressions are equal. For example,

  $8x=24$