Respuesta :
Hello,
Let's assume a the age of Bea
b the age of her sister
This year: a+b=18
Next year (a+1)+(b+1)=(a+b)+(1+1)=(a+b)+2=18+2=20
Let's assume a the age of Bea
b the age of her sister
This year: a+b=18
Next year (a+1)+(b+1)=(a+b)+(1+1)=(a+b)+2=18+2=20
b=bea's age
sister+b=18
next years, both grew 1
sister+1+b+1=18+1+1=20
sum is 20
sister+b=18
next years, both grew 1
sister+1+b+1=18+1+1=20
sum is 20