Roy is twice as old as joan, and in 3 years the sum of their ages will be 21 years. find their present ages.

Roy is 10 years old at present and Joan is 5 years old at present

Step-by-step explanation:

Let

x> Roy's age

y> Joan's age

we know that

x=2y > equation A

(x+3)+(y+3)=21 > equation B

substitute equation A in equation B

(2y+3)+(y+3)=21

solve for y

3y+6=21

3y=21-6

3y=15

y=5 years

Find the value of x

x=2y  > x=2(5)=10 years

therefore

Roy is 10 years old at present

Joan is 5 years old at present