1. A factory produces 40 cakes in N hours.If the factory produces 2 more cakes in each hour , then it will take 1 hour less to produce 40 cakes.Find the values of N.
2. A man rows against the current for a distance of 12 km in a stream flowing at 4km/h.Then he turns round rows back with the current to his starting point.If the whole trip takes 4 hours , find the man's rowing speed in still water.
f.4 quad. equation mark 10!!!!
2009-11-18 5:09 am
回答 (2)
2009-11-18 5:29 am
✔ 最佳答案
(1) Original cakes per hour = 40/NFaster cakes per hour = 40 / (N-1)
Difference in cakes per hour = 40 / (N - 1) - 40 / N = 2
[40N - 40(N - 1)] / [N(N - 1)] = 2
40 = 2N(N - 1)
N^2 - N - 20 = 0
(N - 5)(N + 4) = 0
N = 5 or N = -4 (rejected)
(2) Let the rowing speed be v km/h
Resultant speed against current = (v - 4) km/h
Time to travel 12km = 12 / (v - 4) hours
Resultant speed with the current = (v + 4) km/h
Time to travel 12km = 12 / (v + 4) hours
Total time = 12/(v-4) + 12/(v+4) = 4
[12(v+4)+12(v-4)]/[(v-4)(v+4)] = 4
24v / (v^2 - 16) = 4
v^2 - 16 = 6v
v^2 - 6v - 16 = 0
(v - 8)(v + 2) = 0
v = 8 or v = -2(rejected)
His speed in still water is 8km/h
2009-11-18 5:24 am
1.
(40/N)*(N-1)=40N
2N^2-2N-40=0
N=5 or -4(rej)
2
2009-11-17 21:30:56 補充：
2.
12/(X-4)+12/(X+4)=4
X^2-24X-64=0
X=8 or -2(rej)
(40/N)*(N-1)=40N
2N^2-2N-40=0
N=5 or -4(rej)
2
2009-11-17 21:30:56 補充：
2.
12/(X-4)+12/(X+4)=4
X^2-24X-64=0
X=8 or -2(rej)
收錄日期: 2021-04-23 23:28:40
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