F.3 Maths
2007-11-23 2:33 am
1. 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?
回答 (2)
2007-11-23 2:37 am
✔ 最佳答案
Let $x be the monthly saving of the family in MayThe 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
2007-11-23 2:40 am
Assume monthly saving in May = x
Then monthly saving in June = monthly saving in May * (1-0.1) = 0.9x
Then monthly saving in July = monthly saving in June * (1-0.1) = 0.81x
Total saving = $40650 = x + 0.9x + 0.81x
.'. 2.71x = $40650
x = $15000
.'. The monthly savings of the family in May is $15000.
Then monthly saving in June = monthly saving in May * (1-0.1) = 0.9x
Then monthly saving in July = monthly saving in June * (1-0.1) = 0.81x
Total saving = $40650 = x + 0.9x + 0.81x
.'. 2.71x = $40650
x = $15000
.'. The monthly savings of the family in May is $15000.
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