The diameter of two circles are 18 cm and 8 cm. The distance between their centres is 13 cm. What is the number of common tangents?  Pick one.
A) 3 B) 2 C) 1 D) 5 E) 7
3   3   Here, r1 = 9 cm and r 2 = 4 cm   r 1 + r 2 = 9 + 4= 
<gadget id="calculator">9 + 4</gadget>
<output>13</output>
13 cm   and r 1 – r 2= 9 – 4 = 5cm   3lso, d = 13 cm   Here, d = r 1 + r 2   = 13 cm   Hence, two circles touch each other externally, so three total no of common tangents are three.
<result>A</result>
The diameter of two circles are 18 cm and 8 cm. The distance between their centres is 13 cm. What is the number of common tangents?