How is mathematics related to physics, agriculture, and business studies? Also, if y = 1.34444..., find the value of (y-1)/y.

Let $y = 1.3\overline{4}$.
$$
10y = 13.\overline{4} \quad (1)
$$
$$
100y = 134.\overline{4} \quad (2)
$$
Subtract (1) from (2):
$$
100y - 10y = 134.\overline{4} - 13.\overline{4}
$$
$$
90y = 121
$$
$$
y = \frac{121}{90}
$$

$$
\frac{y-1}{y} = \frac{\frac{121}{90} - 1}{\frac{121}{90}}
$$
$$
\frac{y-1}{y} = \frac{\frac{121}{90} - \frac{90}{90}}{\frac{121}{90}}
$$
$$
\frac{y-1}{y} = \frac{\frac{121 - 90}{90}}{\frac{121}{90}}
$$
$$
\frac{y-1}{y} = \frac{\frac{31}{90}}{\frac{121}{90}}
$$
$$
\frac{y-1}{y} = \frac{31}{90} \times \frac{90}{121}
$$
$$
\frac{y-1}{y} = \frac{31}{121}
$$
The value is $\boxed{\frac{31}{121}}$.

Number of t-shirts: $192 \approx 200$  
Price per t-shirt: $5950 \text{ Tanzanian shillings} \approx 6000 \text{ Tanzanian shillings}$

Estimated total money = Estimated number of t-shirts $\times$ Estimated price per t-shirt  
Estimated total money = $200 \times 6000 \text{ Tanzanian shillings}$  
Estimated total money = $1,200,000 \text{ Tanzanian shillings}$  
The estimated money the shopkeeper got is $\boxed{1,200,000 \text{ Tanzanian shillings}}$.

$$
234 - 35.4 = 198.6
$$

The hundreds digit in 198.6 is 1. The digit to its right is 9. Since 9 is 5 or greater, round up the hundreds digit.  
198.6 rounded to the nearest hundreds is 200.  
The answer is $\boxed{200}$.

Let the total value from 500 shilling coins be $V_{500}$, from 200 shilling coins be $V_{200}$, and from 100 shilling coins be $V_{100}$.  
The ratio $V_{500} : V_{200} : V_{100} = 2:3:5$.  
Let the common multiplier be $x$.  
$V_{500} = 2x$  
$V_{200} = 3x$  
$V_{100} = 5x$

The total amount is $780,000 \text{ Tanzanian shillings}$.
$$
2x + 3x + 5x = 780,000
$$
$$
10x = 780,000
$$
$$
x = \frac{780,000}{10}
$$
$$
x = 78,000
$$

$V_{500} = 2 \times 78,000 = 156,000 \text{ Tanzanian shillings}$  
$V_{200} = 3 \times 78,000 = 234,000 \text{ Tanzanian shillings}$  
$V_{100} = 5 \times 78,000 = 390,000 \text{ Tanzanian shillings}$

Number of 500 shilling coins ($N_{500}$):
$$
N_{500} = \frac{V_{500}}{500} = \frac{156,000}{500} = 312 \text{ coins}
$$
Number of 200 shilling coins ($N_{200}$):
$$
N_{200} = \frac{V_{200}}{200} = \frac{234,000}{200} = 1170 \text{ coins}
$$
Number of 100 shilling coins ($N_{100}$):
$$
N_{100} = \frac{V_{100}}{100} = \frac{390,000}{100} = 3900 \text{ coins}
$$
The number of 500 shilling coins is **312**, the number of 200 shilling coins is **1170**, and the number of 100 shilling coins is **3900**.