隨著年齡的增加，記憶力的減退不可避免，現(xiàn)代生活節(jié)奏的加快，讓失眠也成為多數(shù)人的常態(tài)。睡眠不足，會(huì)給大腦造成不可逆的損傷。比爾蓋茨最近也開始說要早睡。

如果一切不可避免，或許給大腦足夠的鍛煉才是真正的解決之道。

每天AMC五道題，腦力活力沒問題。

1. What is the value of

(A) 7 (B) 21 (C) 49 (D) 64 (E) 91

2. Menkara has a 4x6 index card. If she shortens the length of one side of this card by 1 inch, the card would have area 18 square inches. What would the area of the card be in square inches if instead she shortens the length of the other side by 1 inch?

(A) 16 (B) 17 (C) 18 (D) 19 (E) 20

3. What is the maximum number of balls of clay with radius 2 that can completely fit inside a cube of side length 6 assuming that the balls can be reshaped but not compressed before they are packed in the cube?

(A) 3 (B) 4 (C) 5 (D) 6 (E) 7

4. The six-digit number  is prime for only one digit A. what is A？

(A) 1 (B) 3 (C) 5 (D) 7 (E) 9

5. Elmer the emu takes 44 equal strides to walk between consecutive telephone poles on a rural road. Oscar the ostrich can cover the same distance in 12 equal leaps. The telephone poles are evenly spaced, and the 41st pole along this road is exactly one mile (5280 feet) from the first pole. How much longer, in feet, is Oscar’s leap than Elmer’s stride?

(A) 6 (B) 8 (C) 10 (D) 11 (E) 15