A magician has a top hat with 20 red marbles and a top hat with 30 blue marbles. If he takes away 3 red marbles and four times as many blue marbles as red marbles (without looking), how many marbles in total does he have left?
He had 20 red marbles and took away 3 leaving 20-3 = 
<gadget id="calculator">20-3</gadget>
<output>17</output>
17 red marbles.
He took 4 times as many blue marbles as red marbles which is 4*3 = 
<gadget id="calculator">4*3</gadget>
<output>12</output>
12 blue marbles.
He took 12 blue marbles from 30 leaving 30-12 = 18 blue marbles.
He now has 17+18 = 
<gadget id="calculator">17+18</gadget>
<output>35</output>
35 marbles left.

<result>35</result>