There are 20 sandcastles on Mark's beach, each with 10 towers. On Jeff's beach, there are three times as many castles as on Mark's beach, each with 5 towers. What is the combined total number of sandcastles and towers on Mark's and Jeff's beaches?
The total number of towers at Mark's beach is 20*10 = 
<gadget id="calculator">20*10</gadget>
<output>200</output>
200 towers.
There are 200+20 = 
<gadget id="calculator">200+20</gadget>
<output>220</output>
220 sandcastles and towers on Mark's beach.
Jeff's beach has 3*20 = 
<gadget id="calculator">3*20</gadget>
<output>60</output>
60 sandcastles, three times as many as the number of sandcastles in Mark's beach.
The number of towers in each of the sandcastles on Jeff's beach is 1/2*10 = 
<gadget id="calculator">1/2*10</gadget>
<output>5</output>
5.
Since each sandcastle has 5 towers on Jeff's beach, there are 5*60 = 
<gadget id="calculator">5*60</gadget>
<output>300</output>
300 towers.
In total, on Jeff's beach, there are 300+60 = 
<gadget id="calculator">300+60</gadget>
<output>360</output>
360 towers and sandcastles.
Altogether, 360+220 = 
<gadget id="calculator">360+220</gadget>
<output>580</output>
580 sandcastles and towers can be found on their beaches.

<result>580</result>