a4y8 E se? In un numero di due cifre, la differenza tra il doppio della cifra delle decine e la cifra delle unità è 4 ; la somma tra il numero stesso e il numero che si ottiene invertendone le cifre supera il doppio del numero stesso di 18 . Qual è il numero? Come cambierebbe la risposta se la differenza tra il doppio della cifra delle decine e la cifra delle unità fosse 6 ? [68; impossibile]

a) A box has 12 bulbs, 3 of which are defective. If two bulbs are to be selected at random without replacement, then what. is the probability that both bulbs are defective? b) There are two telephone lines \( A \) and \( B \). Line \( A \) is engaged \( 50 \% \) of the time and line B is engaged \( 60 \% \) of the time. Both lines are engaged \( 30 \% \) of the time. Calculate the probability that only one line is engaged.

OMPARING SIMILAR FIGURES Dilate the figure using the indicated scale facto What is the value of the ratio (new to original) of the perimeters? the areas? ee Exploration 1 , p. 83.) 6. a triangle with vertices \( (0,0),(0,2) \), and \( (2,0) ; k=3 \) 7. a square with vertices \( (0,0),(0,4),(4,4) \), and \( (4,0) ; k=0.5 \)

Evaluate the expression. \[ \frac{4 a+8 b}{7-a^{2}} \quad \text { if } a=3 \text { and } b=-1 \]

The quadratic equation \( y=-16 r^{2}+40 t+2 \) represents the height of a projectile, \( y \), in feet, at a particular time, \( t \), in seconds. For what interval or intorvals of time will the projectilo be above 18 foet? \[ \begin{array}{l}\text { a) Between } 1 \text { and } 1.5 \text { seconds } \\ \text { b) Between } 0.5 \text { and } 2 \text { seconds } \\ \text { a) Less than } 1 \text { second and greater than } 1.5 \text { seconds } \\ \text { di) Less than } 0.5 \text { second and greater than } 2 \text { seconds }\end{array} \]

d) \( \frac{1}{2} X: \frac{5}{4}=\frac{3}{10} \)