A shop sells milkshakes in two sizes. The small milkshake is 300 ml and the large milkshake is 2/3 more than the small milkshake. Find the size of the large milkshake.

Loss is 5% of M40 000.

Selling price is the original price minus the loss.

The selling price is $\boxed{\text{M}38000}$.

The formula for compound interest is $A = P(1 + r)^n$, where $A$ is the final amount, $P$ is the principal amount, $r$ is the annual interest rate, and $n$ is the number of years.
Given $P = \text{M}50000$, $r = 4\% = 0.04$, and $n = 3$ years.

The price of the land after three years is $\boxed{\text{M}56243.20}$.

The large milkshake is $\frac{2}{3}$ more than the small milkshake.

The size of the large milkshake is $\boxed{500 \text{ ml}}$.

Small milkshake : Large milkshake = 300 ml : 500 ml

Divide both sides by 100.

The ratio in its simplest form is $\boxed{3:5}$.

The formula for simple interest is $I = A - P$, where $I$ is the interest, $A$ is the final amount, and $P$ is the principal.
Given $A = \text{M}17400$ and $P = \text{M}12000$.

The formula for simple interest is $I = \frac{PRT}{100}$, where $P$ is the principal, $R$ is the rate, and $T$ is the time in years.
Given $I = \text{M}5400$, $P = \text{M}12000$, and $T = 3$ years.

The value of $r$ is $\boxed{15}$.