= 1/2+( 1/2- 1/4)+( 1/4- 1/8)+( 1/8- 1/65438) 6)+( 1/6- 1/ 12)+( 1/ 12- 1/24)

= 1/2+ 1/2- 1/4+ 1/4- 1/8+ 1/8- 1/ 16+65448

=1-116+1/48 divided by1+1/3+1/24.

=23/24 divided by 13/8

=23/39

Question 2: Let the length of the train be x meters.

It takes 80 seconds for the train to cross the199m bridge.

It is known that the train speed is expressed as (x+ 199)/80m per second.

172m long tunnel takes 72 seconds.

It can be known that the train speed is expressed as (x+ 172)/72 meters per second.

Then there is: (x+199)/80 = (x+172)/72 the solution of the simplified equation itself.

Or:

2) It takes 80 seconds for the train to pass through the bridge of 199m and 72 seconds to pass through the tunnel of 172m at the same speed. Find the speed of the train.

(199-172)/(80-72) = 3.375 (m)

The speed of the train is 3.375 meters per second.

Question 3: (1000-4*80)/(80+5) =? This question mark refers to the answer of this formula.

So add 4, that's (? +4) is all the days required to complete the task.

or

(3) The garment factory should process 1000 suits, 80 suits a day for the first four days, and 5 more suits a day for the rest of the time. How many days will it take to complete these tasks?

(1000-4 * 80)/(80+5)+4 =12 (days)

It takes 12 days to complete these tasks.