1).The TV station broadcasts 16 hours every day. 20% of the time os for advertisements, 40% for news and 40% for music programmes. If the total time for advertisements and news is incease by 20%, what is the percentage decrease time for music programmes?
2). An alloy, which contains 70%iron and 30% aluminium, weighs 20kg. If add 5 kg copper into the alloy, what percentages are iron, aluminium and coppr in the mew alloy respectively?
Please show the work out and explan!!! Thanks!!!
Maths Question!! 20 points!!!!!!
2008-09-13 9:23 pm
回答 (3)
2008-09-13 9:58 pm
✔ 最佳答案
1. New total time for advertisements and news
= (16 h) x (20% + 40%) x (1 + 20%)
= 11.52 h
New time for music programmes
= (16 - 11.52) h
= 4.48 h
Original time for music programmes
= 16 h x 40%
= 6.4 h
Precentage decrease time for music programmes
= [(6.4 - 4.48)/6.4] x 100%
= 30%
=====
2.
Mass of iron in the new alloy
= Mass of iron in the original alloy
= (20 kg) x 70%
= 14 kg
Mass of aluminium in the new alloy
= Mass of aluminium in original alloy
= (20 kg) x 30%
= 6 kg
Mass of copper in the new alloy
= 5 kg
Total mass of the new alloy
= (20 + 5) kg
= 25 kg
Percentage of iron in the new alloy
= (14/25) x 100%
= 56%
Percentage of aluminium in the new alloy
= (6/25) x 100%
= 24%
Percentage of copper in the new alloy
= (5/5) x 100%
= 20%
Ans: The new alloy contains 56% iron, 24% aluminium and 20% copper.
=
2008-09-13 9:36 pm
1)
原本:
advertisement + news: 60% = 9.6h
music: 6.4h
之後:
advertisement + news: 9.6*120%=11.52
music: 16-11.52=4.48
2)
iron: 14kg 56%
aluminium: 6kg 24%
copper: 5kg 20%
total: 25kg 100%
原本:
advertisement + news: 60% = 9.6h
music: 6.4h
之後:
advertisement + news: 9.6*120%=11.52
music: 16-11.52=4.48
2)
iron: 14kg 56%
aluminium: 6kg 24%
copper: 5kg 20%
total: 25kg 100%
參考: me
2008-09-13 9:24 pm
20mm
). An alloy, which contains 70%iron
). An alloy, which contains 70%iron
收錄日期: 2021-04-24 09:52:04
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