帮我做下.顺便讲下为什么2.Asumofmoneyisdepositedinabankfor2yearsataninterestrateof8%p.a.compoundedyearly.Iftheinterestearned（赚）after2yearsis$12480.Findtheprincipal.（本金）(5marks)3.50isin

Question

帮我做下.顺便讲下为什么
2. A sum of money is deposited in a bank for 2 years at an interest rate of 8% p.a. compounded yearly. If the interest earned（赚） after 2 years is $12480. Find the principal.（本金）(5marks)



3. 50 is increased by 7% and then decreased by 7%. (8marks)
(1)Find the final value (2)Find the percentage change

Answer 1

Assume that the principal is x.
so x*（1+8%）^2=$12480 x=10700（约等于）
so the principal is 10700.
50*（1+7%）*（1-7%）=49.755 （50-49.755）/50=0.49%
so the final value is 49.755
the percentage change is 0.49%
第一问是已知本利和复利求本金,第二问是求50变动两次的最终值和变动的最终百分比.
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