Question

Four years ago, the average age of a family of four persons was $18$ years. During this period, a baby was born. Today if the average age of the family is still $18$ years, the age of the baby is

• A. $1.2$ years
• B. $2$ years
• C. $2.5$ years
• D. $3$ years

Answer 1

The correct option is B $2$ years

Sum of the ages of $4$ members, four years ago $=18\times 4=72$ years
Sum of the ages of $4$ members now $=72+4\times 4=88$ years
Sum of the ages of $5$ members now
$=18\times 5=90$ years
$\therefore$ Age of the baby $=90-88=2$ years