Question: 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 ?
A) 4
B) 10
C) 12
D) 14
E) 16
Correct answer: a
Grade: 7 | Topic: Expressions and Equations | Difficulty: Hard | Standard: 7.EE.B.4