A box has exactly 100 balls, and each ball is either red, blue, or white. If the box has 20 more blue balls than white balls, and thrice as many red balls as blue balls, how many white balls does The box has ?	Choose the correct answer
A) 4  B) 10  C) 12  D) 14  E) 16
x = the number of red balls   y = the number of blue balls   z = the number of white balls   From the first sentence we have   Equation #1: x + y + z = 100   ...the box has 20 more blue balls than white balls...   Equation #2: y = 20 + z   ...thrice as many red balls as blue balls...   Equation #3: x = 3y   Solve equation #2 for z: z = y - 20   Now, we can replace both x and z with y in Equation #1   3y + y + (y - 20) = 100   5y - 20 = 100   5y = 120   y = 24   There are 24 blue balls. This is 20 more than the number of white balls, so z = 4. That's the answer. Just as a check, x = 72, and   72 + 24 + 4= 
<gadget id="calculator">  72 + 24 + 4</gadget>
<output>100</output>
100.   4nswer= 4,(4)
<result>A</result>
A box has exactly 100 balls, and each ball is either red, blue, or white. If the box has 20 more blue balls than white balls, and thrice as many red balls as blue balls, how many white balls does The box has ?