Question

Barbara's sister is twice as old as Barbara. Barbara's sister is 7 years younger than Barbara's brother. If Barbara's brother is 21, which equation could be used to find Barbara's age (b)?

Answer 1

To find Barbara's age, we can set up an equation using the given information. By substituting the known values and solving, we find that Barbara's age is 7 years.

Step-by-step explanation:

To find Barbara's age (b), we need to use the given information. Let's break down the problem:

1. Barbara's sister is twice as old as Barbara. This means, Sister's age = 2 * Barbara's age.
2. Barbara's sister is 7 years younger than Barbara's brother. This means, Sister's age = Brother's age - 7.
3. We know Barbara's brother's age is 21.

We can set up an equation to find Barbara's age:

Sister's age = 2 * Barbara's age

Sister's age = Brother's age - 7

Substituting the known values, we get:

2 * Barbara's age = 21 - 7

2 * Barbara's age = 14

Dividing both sides by 2, we get:

Barbara's age = 14 / 2

Therefore, Barbara's age is 7 years.

Answer 2

Option D

Step-by-step explanation:

Let the age of Barbara sister = x years

And the age of Barbara's brother = y years

"Barbara's sister is 7 years younger than Barbara's brother"

x = y - 7

If y = 21,

x = 21 - 7 ------(1)

"Barbara's sister is twice old as Barbara"

x = 2b --------(2)

By substituting the value of x from equation (2) to equation (1),

2b = 21 - 7

2b + 7 = 21 + 7

2b + 7 = 21

Therefore, Option D will be the answer.