2 If the lengths of the two parallel bases of a trapezium are \( 15 \mathrm{~cm} ., 11 \mathrm{~cm} \)., then the length of its middle base is \( \ldots \ldots \ldots \ldots . . . \mathrm{cm} \). \( \begin{array}{llll}\text { (a) } 4 & \text { (b) } 26 & \text { (c) } 13 & \text { (d) } 12\end{array} \)

To find the length of the middle base of a trapezium with parallel bases of \( 15 \, \text{cm} \) and \( 11 \, \text{cm} \), you can use the average of the two bases: \[ \text{Middle Base} = \frac{\text{Base}_1 + \text{Base}_2}{2} = \frac{15 \, \text{cm} + 11 \, \text{cm}}{2} = \frac{26 \, \text{cm}}{2} = 13 \, \text{cm}. \] So the answer is \( \text{(c) } 13 \, \text{cm} \). When dealing with trapeziums, a common mistake is to confuse the middle base with the height. Remember, the middle base is simply the average of the lengths of the two parallel sides. It's easy to overlook that the bases can have different lengths while still forming a trapezium!