A box contains 156 rubber bands. There are 100 yellow rubber bands and the rest are green or red. The green ones are 3 times as many as the red ones.
(i) Find the number of green bands.
(ii) Find the probability of getting a red band if a band is randomly chosen from the box
(iii) y red bands are added to the box. The probability of part (ii) becomes 10/81. Find y.
Probabilities
2011-05-23 7:05 am
回答 (1)
2011-05-23 7:18 am
✔ 最佳答案
i)
156 - 100 = 56 (green and red) rubber bands.
56 x 3/(3 + 1)
= 42 green rubber bands.
ii)
P(getting a red)
= (156 - 100 - 42) / 156
= 7 / 78
iii)
((156 - 100 - 42) + y) / (156 + y) = 10/81
10(156 + y) = 81(14 + y)
y = 6
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