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On-line mathematical problem solving
1. Two thirds of boys are 40 years younger than four fifths of girls.

Then 5/6 boys are 50 less than girls.

(3 14-50)/[ 1+(5/6)]

=264/( 1 1/6)

= 144 (human) boy

314-144 =170 (female)

2. What is left after A's work: 1-( 1/20)*4=4/5.

(4/5)/( 1/30)=24 (days)

3. Set the c x yuan

6x+ 180= 1.5*(5x+30)

1.5x= 135

x = 90°

90*( 1+5+6)= 1080 (yuan)

4.400*2/(280-240)=20 (minutes)

5. Ergonomics of (112) * 2 =1/6 b

1/[(112)+(1/6)] = 4 (days)

6. Work efficiency of both parties: (2/3)/4= 1/6.

The working efficiency of A is 1/8.

Ergonomics of B:1/6-1/8 =1/24.

1/( 1/24)=24 (days)

7. Working efficiency of Team A, Team B, Team C and Team III:1/2 * (1/6+1/4+1/8) =13/48.

A:13/48-1/4 =1/48 48 days.

B:13/48-1/8 = 7/48 48/7 days.

C:13/48-1/6 = 5/48 9.6 days.

8.2 minutes left

1-( 1/5+ 1/ 10- 1/ 15)*2==8/ 15

(8/15)/(1/5-115) = 4 (days)