Grades 3-4 Video Solutions 2021-video 2021 3-4/8

Video Transcription

Problem number 8. Rosanna has 7 balls of 3 different colors. Balls of the same color have the same weight. What is the weight of each white ball?  A-3 kg, B-4 kg, C-5 kg, D-6 kg, or E-7 kg If we look at the first scale here, we see that we have a black one and a grey one. Those two balls weigh 6 kg together.  If we look at the third scale, we see we have the same colors except another grey one. That makes 10.  Now, if these two together make 6 kg, this grey one has to weigh 4, because 6 plus 4 is 10.  And if we look at the second scale, we see that it all adds up to 14.  And we know that the grey balls weigh 4, and these two white balls are the same, and there's only 10 kg left now to figure out.  So these each have to weigh 5 kg. So our answer is C, 5 kg.

Video Summary

Rosanna has 7 balls of 3 different colors with same colors having equal weights. To find the weight of each white ball, we analyze the scales. The first scale shows a black and a grey ball weighing 6 kg together. The third scale adds another grey ball for a total of 10 kg, indicating each grey ball weighs 4 kg. On the second scale, two grey and two white balls total 14 kg. Subtracting the grey weights (8 kg) leaves 6 kg shared by two white balls, making each white ball weigh 5 kg. Thus, each white ball weighs 5 kg, option C.

Keywords

ball weights

color balls

weight analysis

scale measurement

white ball weight