扫描二维码，直接登录
题库 / Prep2007E1-DS-144
If $1,000 is deposited in a certain bank account and remains in the account along with any accumulated interest, the dollar amount of interest, I , earned by the deposit in the first n years is given by the formula I =1000〔(1 + ~$\frac{r}{100}$~ )n - 1〕 , where r percent is the annual interest rate paid by the bank. Is the annual interest rate paid by the bank greater than 8 percent?
(1) The deposit earns a total of $210 in interest in the first two years.
(2) ( 1 + ~$\frac{r}{100}$~ )2 > 1.15
Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
EACH statement ALONE is sufficient.
Statements (1) and (2) TOGETHER are NOT sufficient.
这里说个计算捷径——（从gmatclub 来的）
Shortcut to multiply numbers of the form (100 + a) or (100 - a)
Write a2a2 on the right hand side. Add a to the original number and write it on left side. The square is ready.
e.g. 1082=(100+8)21082=(100+8)2 Write 64 on right hand side
________ 64
Add 8 to 108 to get 116 and write that on left hand side
11664 - Square of 108
e.g. 912=(100−9)2912=(100−9)2 => ______81 => 8281
(Here, subtract 9 from 91)
Note: a could be a two digit number as well.
e.g 1122=(100+12)21122=(100+12)2 = ______44 => 12544
(Only last two digit of the square of 12 are written on the right hand side. The 1 of 144 is carried over and added to 112 + 12)
This is Vedic Math though the trick uses basic algebra.
(100+a)2=10000+200a+a2(100+a)2=10000+200a+a2
(100 + 8)^2 = 10000 + 200 x 8 + 64 = 10000 + 1600 + 64 = 11664
This is a useful trick that saves time.
(2) (1 + r/100 )^2 > 1.15 --> if r=8 then (1+r/100)^2=(1+8/100)^2=1.08^2≈1.16>1.15
so, if r is slightly less than 8 (for example 7.99999), (1+r/100)^2 will still be more than 1.15. So, this statement is not sufficient to say whether r>8.
登录 或 注册 后可以参加讨论