Two men undertake a piece of work for $600. Individually, they can complete the work in 6 days and 8 days, respectively. With the assistance of a boy they completed the work in 3 days. The boy's share should be:

? In 5 days , (4 men + 6 women ) get ? 1600.
? In 1 day, (4 men + 6 women) get ? 1600/5 = ? 320 ....(i)

In 1 day number of person to get ? 1 = 320 / 4 men + 6 women ....(ii)

Similarly, in second condition,
In 1 day, number of person to get ? 1 = (1740 / 6) x (3 men + 7 women)
= 290 / (3 men + 7 women) ....(iii)

From Eqs. (ii) and (iii), we get
320 / (4 men + 6 women) = 290 / (3 men + 7 women)
96 men + 224 women = 116 men + 174 women
? 20 men = 50 women
? Man / Women = 5/2
? 1 women = 2/5 man
From Eq. (i), 1 day,
(4 men + 6 women) = (4 men + 6 x 2/5 men) = 32/5 men get ? 320
? In 1 day, 1 man get = 320 x 5 /32 = ? 50
? In 1 day, 1 woman get = 50 x 2/5 = ? 20
? In 1 day, (7 men + 6 women) get
7 x 50 + 6 x 20 = ? 470
? Required number of days = 3760 / 470 = 8 days

Work for 1 st 2 days = (1/8) + (1/12) = 5/24
? Work for 8 days = (5/24) x (8/2) = 5/6
? Remaining work = 1- (5/6) = (6 - 5) / 6 = 1/6
On 9th day, A's work = 1/8

Remaining work after 9 days = (1/6) - (1/8) = (4 - 3) / 24 = 1/24
B will finish this work in (12 x 1)/24 = 1/2 day
Clearly, A worked for 5 days from starting.

? Work done by A in 5 days = (1/8) x 5 = 5/8
? A's share = (5/8) x 1280 = 5 x 160 = ? 800

Let man be represented by m and woman be represented by w.
? 2m + 1w = 1/14
? 14 x (2m + 1w ) = 1 ...(i)

and 4w + 2m = 1/8
8 x (4w + 2m) = 1 ...(ii)

On equating Eqs. (i) and (ii), we get
14 (2m + 1w) = 8 (4w + 2m)
? 28m + 14w = 32w + 16m
? 28m - 16m = 32w - 14w
? 12m = 18w
? m/w = 18/12 = 3/2
So, efficiency of 1 man and 1 woman is 3 : 2.
So, their wages must be in the same ratio
90/x = 3/2
[here, x = wages of a woman ]
? x = 90 x 2 / 3 = ? 60

Let the numbers of men, women and
children are 3k, 2k and k, respectively.
Given, 3k = 90
? k = 30
Number of women = 60
and number of children = 30

Let the men's, women's and children's
wages be ? 5p, ? 3p and ? 2p, respectively.
According to the question,
Total daily wages = ? 10350
? 90 x 5p + 60 x 3p + 30 x 2p = 10350
? p x (450 + 180 + 60) = 10350
? p = 10350/690 = 15
? Daily wages of a man = 15 x 5 = ? 75

By investing Rs 96, income derived = Rs. 9/2
By investing Rs. 100, income derived = Rs. (9 x 100) / (2 x 96) = Rs.4.69
Interest obtained =4.69%