數學..pls help me

1. Dante went to the store to buy 2 gallons of milk. He can buy the
milk in quart containers for $0.79 or in gallon container for $2.50.
How much can he save by buying the milk in gallon containers?
Sol:
1 gallon ＝ 4 quarts
0.79 × 4 ＝ 3.16
2 × ( 3.16 － 2.5 )
＝ 2 × 0.66
＝ 1.32
Ans: $1.32
2. There is a large cube of ice weighing 256 pounds. It has edges
that are 4 feet in length. If the cube melts at the rate of 3 inches
every 15 minutes, how long will it take for the cube to weight 32
pounds?
Sol:
1 feet ＝ 12 inches
32 ÷ 256 ＝ 1/8 ＝ (1/2)3
therefore, the length of the cube is halved of original cube after melt.
2 × 1/2 ＝ 1 ....... melt 1 feet
12 ÷ 3 × 15
＝ 60
Ans: 60 minutes
3. A 3/4 mile long train is traveling at 25 miles per hour. It has to
cross a bridge that is 2 miles in length. How long will it take the

whole train to completely cross the bridge?
Sol:
2 ＋ 3/4
＝ 2.75 ....... the length for the train to pass
2.75 ÷ 25
＝ 0.11
0.11 hour ＝ 6.6 minutes ＝ 6 minutes 36 seconds
Ans: 6 minutes 36 seconds
If any steps you don’t understand, send me a letter, thank you.

1.

1 gallon = 4 quarts

0.79 × 4 = 3.16

2 × ( 3.16 - 2.5 )

= 2 × 0.66

= 1.32

2.

1 feet = 12 inches

32 ÷ 256 = 1/8 = (1/2)^3

2 × 1/2 = 1

12 ÷ 3 × 15

= 60

3.

2 + 3/4

= 2.75 ....... the length for the train to pass

2.75 ÷ 25

= 0.11