Solution:21. (d): Let present age of mother and son be “x” and “y” years respectively.
Then,
x − 1 = 4(y − 1)
⇒ x = 4y − 3 ...(i)
And,
x + 6 = 2(y + 6) + 5 ...(ii)
⇒ 4y − 3 = 2y + 11
⇒ y = 14/2 = 7 years
And, x = 25 years
And, Required ratio = 25 : 7