Maths!!!!!!!Quick!!!!!!!!!!!

Maths!!!!!!!Quick!!! !!!!!!!!
1) Alice had some $10 banknotes, $ 20 banknotes and $100 banknotes. The number of $10 banknotes is 3 times that of $20 banknotes.The number of $20 banknotes is 8 times that of $100 banknotes. If Alice had $1500, find the number of $100 banknotes she had.


設有 x 張100元，則有8x張20元及24x張10元
則
100x + 20*8x + 10*24x = 1500
100x + 160x + 240x = 1500
500x = 1500
x = 3
他有3張100元

2) Water flows from a pipe r over 27 L per minute. Find the amount of water supply in r2 hours.
(r/27) x r2 x 60
= 20r3 / 9

1) Let the number of $100 banknote Alice had be X
Alice had 8X $20 banknotes
Alice had 24X $10 banknotes (24X = 3 * 8X)

10(24X) + 20(8X) + 100X = 1500
240X + 160X + 100X = 1500
500X = 1500
X = 3

2) the required amount of water supply = (r / 27) * (r^2 * 60) = (20r^3)/9 LITER

1) Let x be the number of $100 banknote
the number of $20 banknote is 8(x)=8x
the number of $10 banknote is 3(8x)=24x

24x(10)+16x(20)+100x=1500
240x+160x+100x=1500
500x=1500
500x/500=1500/500
x=3
so the number of $100 banknote is 3