Alfred had a sum of money on Monday. He spent $10 each day and saved half of the money left on that day. After he spent $10 on Friday, he had no more money left. How much did he originally have on Monday?
Please use equation to answer this question beacause i have found the answer by using my own way.
A maths question?
2015-09-05 6:07 am
回答 (1)
2015-09-05 2:42 pm
Let $y be the amount he originally had on Monday.
Amount left on Monday = (1/2)(y - 10) = (1/2)y - 5
Amount left on Tuesday = (1/2)[(1/2)y - 5 - 10] = (1/4)y - (15/2)
Amount left on Wednesday = (1/2)[ (1/4)y - (15/2) - 10] = (1/8)y - (35/4)
Amount left on Thursday = (1/2)[(1/8)y - (35/4) - 10] = (1/16)y - (75/8)
(1/16)y - (75/8) = 10
(1/16)y - (375/40) = (400/40)
(1/16)y = (775/40)
y = (775/40) × 16
y = 310
Ans.: He originally had $310 on Monday.
Amount left on Monday = (1/2)(y - 10) = (1/2)y - 5
Amount left on Tuesday = (1/2)[(1/2)y - 5 - 10] = (1/4)y - (15/2)
Amount left on Wednesday = (1/2)[ (1/4)y - (15/2) - 10] = (1/8)y - (35/4)
Amount left on Thursday = (1/2)[(1/8)y - (35/4) - 10] = (1/16)y - (75/8)
(1/16)y - (75/8) = 10
(1/16)y - (375/40) = (400/40)
(1/16)y = (775/40)
y = (775/40) × 16
y = 310
Ans.: He originally had $310 on Monday.
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