The ratio between the present ages of A and B is 4 : 5. If the ratio between their ages 4 yr hence become 14 : 17, Then what is B's age at present?

? Total age of 8 children = 8 x 12 = 96 yr
And total age of 7 children = 12 + 8 + 14 + 11 + 9 + 13 + 15 = 82
? The age of 8th child = 96 - 82 = 14 yr

Required ratio = (36 - 8)/(24 - 8) = 28/16 = 7 : 4

Length of the train = 280 m
Length of the platform = 280 x 3 = 840 m
Taken time = 6 min 40 s = (360 + 40) s = 400 s
? Required speed = Distance / Time = (840 + 280)/400
= 1120/400 = 2.8 m/s

Let my present age be x years.
? x - 20 = x / 3
? 3x - 60 = x
? 2x = 60
? My present age = x = 30 years

Let B;s age 2 years ago be N years
? A's present age = 2N years

From question, 2N - (N + 2) = 2
? N = 4
? A's age = 2 x 4 = 8 years

Let present ages of indira and Lizzy are 3k yr and 8k yr, respectively.
? 3k + 8 = 20 ? 3k = 12
? k = 4
Hence, Lizzy's required age = 8k - 5
= 32 - 5
= 27 yr

Let 7 yr ago, ages of A and B 4k yr and 5k yr, respectively.
Then, present age of A = 4k + 7
and present age of B = 5k + 7
Now, according to the question,
? (4k + 7 + 7) / (5k + 7 + 7) = 5/6
? 24k + 84 = 25k + 70
? k = 14
Hence, B's present age = 5 x 14 + 7 = 77 yr

Let Sarita;s present age = k yr
Then, Kavita's present age = 2k yr
According to the question,
(2k + 8) / (k + 8) = 22/13
? 26k + 104 = 22k + 176
? 4k = 72
? k = 18
Hence, Kavita's age = 2 x 18 = 36 yr

According to the question,
(36 + n) / (50 + n) = 3/4
? 144 + 4n = 150 + 3n
? n = 6

Let the present of Meena and Seema are 7k yr and 8k yr, respectively.
? 8k - 7k = 3
? k = 3
Hence, required sum = 8k + 7k
= 15 x 3 = 45 yr