3道数学题，管卫东里面的，请大家帮忙看看

ARCHER420

 

Q33:

Enrollment in City College in 1980 was 83? percent of enrollment in 1990.  What was the percent increase in the college’s enrollment from 1980 to 1990?



A.     10%

B.     16?%

C.     20%

D.     25%

E.      183?%

Q30:

Joanna bought only $0.15 stamps and $0.29 stamps.  How many $0.15 stamps did she buy?

(1)     She bought $4.40 worth of stamps.

(2)     She bought an equal number of $0.15 stamps and $0.29 stamps.

                   

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D. EACH statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

Q4:

√[2√63 + 2/(8+3√7)] =



A.     8 + 3√7

B.     4 + 3√7

C.     8

D.     4

E.      √7

nicolewitch

B,A,3 do not understand the sign you presented

zscsl

如题

ARCHER420

aawwzzd兄弟数学好牛啊，多谢了！

aawwzzd

第三题：√[2√63 + 2/(8+3√7)]=√{2√63 + 2*(8-3√7)/[(8+3√7)*(8-3√7)]}=√{2√63 + 16-2√63)/(64-63)}=√{2√63 + 16-2√63)=√16=4
注意在倒数第二步中3√7=2√63

lisa8899

I agree with A

aawwzzd

15y<=440 -->y can be 0,5,10,15 .
写错了 应该是：29y<=440 -->y can be 0,5,10,15 .

aawwzzd

A
1). Total amount is $4.4, let x and y the number of two types of stamps. 0.15x+0.29y=4.4 --> 15x+29y=440. The question implies x and y must be integers. The last digit of 15x must be 0 or 5 -->the last digit of 29y must be 0 or 5 and 15y<=440 -->y can be 0,5,10,15 .
If y=0, 5 or 15, x can't be integer -->no,
If y=10, x=10, bingo.
2) Not sufficient obviously

lisa8899

C,D,D