Joe completed 28 math problem from his homework. joe has done 80% of his homework. how many more math problem does joe have to complete

0% = 0.8

 divide 28 by 0.8

28 / 0.8 = 35 total questions

35 -28 = 7 more questions to do

the sum of siblings' ages is 25 years

Solution given:

let the age of brother be x and sister age be y.

By question at the present age of the brother is 5 years older than his sister. in the equation,

it can be  written as:

x=y+5[1]

again;

Before 4 years

sister's age will be y-4.

brother's age will be y-4+5=y+1

Since their ages 4 years ago were the same as 3: 2.

so according to the question.

3(y-4)=2(y+1)

solving the equation, we get

3y-12=2y=2

3y-2y=2+12

y=14

Before 4 years ago the age of sister is y=14-4=10 years

and the present age of brother is x=y+5=10+5=15 years

now

the sum of siblings' ages=x+y=10+15=25 years