The monthly savings of a family decreased at a rate of 10% per month from May this year. If the total savings of the family for May, June and July were $40650, what were the monthly savings of the family in May?
question from exploring mathematics 3A p131 SuppEx4 (#20)
F.3 MATHS_ PERCENTAGE
2006-10-19 9:23 pm
回答 (3)
2006-10-19 9:28 pm
✔ 最佳答案
Let x be the monthly savings of the family in Mayx + x(1-10%) + x(1-10%)(1-10%) = 40650
x + 0.9x + 0.81x = 40650
2.71x= 40650
x= 15000
the monthly savings of the family in May is $15000
參考: me
2006-10-20 1:30 am
Let $x be the monthly saving at May
Then
The monthly saving in June = x(1-10%) = 0.9x
The monthly saving in July = x(1-10%)(1-10%) = 0.9．0.9x = 0.81x
∴x + 0.9x + 0.81x = 40650
2.71x = 40650
x = 40650 / 2.71
x = 15000
∴ The monthly savings of the family in May is $15000
Then
The monthly saving in June = x(1-10%) = 0.9x
The monthly saving in July = x(1-10%)(1-10%) = 0.9．0.9x = 0.81x
∴x + 0.9x + 0.81x = 40650
2.71x = 40650
x = 40650 / 2.71
x = 15000
∴ The monthly savings of the family in May is $15000
2006-10-19 9:31 pm
Let X be the monthly saving at May
Then
X(1-10%) = 0.9X will be the monthly saving at June
0.9X(1-10%) = 0.81X will be the monthly saving at July.
Now,
X + 0.9X + 0.81X = $40650
2.71X = $40650
X = $15000
Therefore, monthly savings of the family in May is $15000
Then
X(1-10%) = 0.9X will be the monthly saving at June
0.9X(1-10%) = 0.81X will be the monthly saving at July.
Now,
X + 0.9X + 0.81X = $40650
2.71X = $40650
X = $15000
Therefore, monthly savings of the family in May is $15000
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