If 12 men and 13 boys can earn $3,720 in 3 days, while 5 men and 6 boys can earn $2,700 dollars in 5 days, how long will it take for 3 men and 4 boys to earn $2,380?
Bonus Question: Can you solve this without working out how much does a man or a boy earn per day?
5m + 6b = 2700/5
12m + 13b = 3720/3
9 times the first equation minus 2 times the second gives:
21m + 28b = 2380
Dividing by 7 gives:
3 m + 4 b = 340 $/day
2380/340 = 7 days (obviously, since we divided the first 2380 by 7).
Why 9 and 2?
FOR i = 40 TO 40
FOR j = 40 TO 40
m = 12 * i + 5 * j
b = 13 * i + 6 * j
IF 4 * m = 3 * b THEN
PRINT i, j
PRINT m, b: PRINT
END IF
NEXT
NEXT
prints, in part:
2 9
21 28

Posted by Charlie
on 20060914 14:02:05 