Question

sisters age is 5 times that of her brothers. After 7 years the sister shall be thrice as old as her brother. How many
years before the sister age was 15 times of her brother age​

Answer 1

Step-by-step explanation:

Let The Brother Age Be X

so, Sister age will be 5X

5X + 7 = 3 ( X + 7 )

5X + 7 = 3X + 21

2X = 14

X = 7.

Answer 2

Given:

Sisters age = 5 times that of her brother's. After 7 years:  sister's age thrice as old as her brother

To find:

The number of years before the sister's age was 15 times of her brother's age​

Solution:

Let the sister's age be x and brother's age be y

So, according to the given condition,

x= 5y------(i)

Also,

(x+7) = 3(y+7) --------(ii)

So, replacing the value of x from equation (i):

5y+7 = 3(y+7)

Or, 5y+7 = 3y+21

Or, 2y = 14

Or, y= 7 (brother)

So, x= 35 (sister)

Next condition:

Let the number of required years be z

(35-z) = 15( 7-z)

So, 35-z= 105 -15z

Or, 14z= 70

Or, z= 5

So, the required no.of years is 5

Before 5 years, the sister's age was 15 times of her brother's age​.