標題:
中一數學4條問題 多謝大家
發問:
求式..1. Road A is twice as long as Road B and Road C is 3.5 km shorter than three times the length of Road B. If the total of the three roads is 47.5km, find the length of each road.2. Mary and her uncle are now 14 and 54 years old respectively.(a.) How many years later will Mary's uncle be 3times as old a... 顯示更多 求式.. 1. Road A is twice as long as Road B and Road C is 3.5 km shorter than three times the length of Road B. If the total of the three roads is 47.5km, find the length of each road. 2. Mary and her uncle are now 14 and 54 years old respectively. (a.) How many years later will Mary's uncle be 3times as old a Mary? (b) How many years ago was Mary's age 1over5 of her uncle's age ? 3. A company decides to produce a batch of eletronic photo-frames. If the jobs is to be done by Factory A,15 days are required . But it takes only 10 days by Factory B. It is known that Factory A and Factory B together can produce 1250 eletronic photo-frames each day. (a) Find the number of eletronic photo-frames produced in the batch. (b) Can the two factories together produce the batch of eletronic photo-frams within 5 days? 4a) 1.5(2-X)=0.4(2X+3)-5(0.5X-1) 4b) 1over6[2X-3over8(X+1)]=11-1over2(X-1) 更新: 4b. 1/6 [2X-3/8(X+1)]=11-1/2(X-1)
最佳解答:
1.B=A/2 C=3B-3.5=3A/2-3.5 A+B+C=47.5 A+A/2+3A/2-3.5=47.5 2A+A+3A-7=95(全式x2) 6A=102 A=17 B=8.5 C=22 2.Let X be the required year (i) (54+X)/(14+X)=3 54+X=42+3X 2X=12 X=6 (ii) Let Y be the required year (14+Y)/(54+Y)=1/5 70+5Y=54+Y 4Y=-16 Y=-4(because it is past) 3.(i)Let A be the required eletronic photo-frames the number of factory A can produce per day=X/15 the number of factory B can produce per day=X/10 X/15 + X/10 =1250 5X=37500(全式x30) X=7500 (ii) 7500/1250=6>5, so they cannot 4(a)1.5(2-X)=0.4(2X+3)-5(0.5X-1) 3-1.5X=0.8+1.2X-2.5X+5 -0.2X=2.8 X=-14 可否清楚點表明4b的題目,因為我弄不清乘除的關係,麻煩你
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4b) 1over6[2X-3over8(X+1)]=11-1over2(X-1) 1/6 [2X-3/8(X+1)]=11-1/2(X-1)
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