1. Choose the correct answer from the given ones : \( \begin{array}{llll}\text { 1 If } X=\{2\}, Y=\{3,4\} \text {, then } n\left(X^{2}\right) \times \mathrm{n}(\mathrm{Y})=\ldots \ldots \ldots \ldots \\ \begin{array}{llll}\text { (a) } 1 & \text { (b) } 2 & \text { (c) } 3 & \text { (d) } 4\end{array}\end{array} \).

La cantidad de un material radiactivo disminuye a la mitad cada 10 años. Si comenzamos con 80 gramos, ¿cuánto quedará después de 30 años?

Expand the logarithm fully using the properties of logs. Express the final answer in terms of \( \log x \). \[ \log 8 x^{3} \] Answer Attempt 1 out of 2

\( \frac{21}{35}=\frac{}{100} \)

3 The middle proportional between the two numbers 3 and 12 is ............. \( \begin{array}{llll}\text { (a) } \pm 3 & \text { (b) } \pm 4 & \text { (c) } \pm 6 & \text { (d) } \pm 12\end{array} \)

\[ S_{n}=1+2+3+\cdots+n \] Calcule \( S_{278} \)