A hippopotamus had a mass of $29.4$ kg at birth. At two months old, it had a mass of $78.9$ kg. We need to find the percentage increase in its mass over these two months, rounded to the nearest $1\%$.

1. Problem Description

A hippopotamus had a mass of $29.4$ kg at birth. At two months old, it had a mass of $78.9$ kg. We need to find the percentage increase in its mass over these two months, rounded to the nearest $1\%$.

2. Solution Steps

First, we calculate the increase in mass.

$Increase = Final Mass - Initial Mass$

$Increase = 78.9 - 29.4 = 49.5$ kg

Next, we calculate the percentage increase.

$Percentage Increase = (Increase / Initial Mass) * 100$

$Percentage Increase = (49.5 / 29.4) * 100$

$Percentage Increase = 1.683673469 * 100$

$Percentage Increase = 168.3673469$

Now, we round the percentage increase to the nearest $1\%$.

$Rounded Percentage Increase = 168\%$

3. Final Answer

The hippopotamus's mass increased by approximately 168%.