I started by adding up all the marbles: 3 black + 6 gold + 2 purple + 6 red = 17 total marbles (not including white). I knew that with white added, the probability of getting a black or gold marble would be 3/7. Then, I knew that 3 black + 6 gold = 9 marbles and 3 x 3 = 9 and 7 x 3 = 21 making 9/21. I just sort of saw this relation between the original fraction and the amount of marbles (black and gold). 21 - 17 = 4 marbles - therefore, Mark put in 4 white marbles. To double check it, it added 3 black + 6 gold + 2 purple + 6 red + 4 white = 21 marbles in all. The black and gold marbles = 9 marbles so picking a black or gold would be 9/21, and that reduced is 3/7 (since 9/3 = 3 and 21/3 = 7).
Hi Katherine, Great Effort! Let me know if the problems I am posting are challenging enough. The questions I have posted over the summer are Level C or gr. 7/8.
I started by adding up all the marbles: 3 black + 6 gold + 2 purple + 6 red = 17 total marbles (not including white). I knew that with white added, the probability of getting a black or gold marble would be 3/7. Then, I knew that 3 black + 6 gold = 9 marbles and 3 x 3 = 9 and 7 x 3 = 21 making 9/21. I just sort of saw this relation between the original fraction and the amount of marbles (black and gold). 21 - 17 = 4 marbles - therefore, Mark put in 4 white marbles.
ReplyDeleteTo double check it, it added 3 black + 6 gold + 2 purple + 6 red + 4 white = 21 marbles in all. The black and gold marbles = 9 marbles so picking a black or gold would be 9/21, and that reduced is 3/7 (since 9/3 = 3 and 21/3 = 7).
Hi Katherine,
ReplyDeleteGreat Effort! Let me know if the problems I am posting are challenging enough. The questions I have posted over the summer are Level C or gr. 7/8.
Okay, thanks. So far they seem to be a good level.
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