48 km downstream, 5 hours upstream 16 km.

32 kilometers downstream and 24 kilometers upstream, it takes 5 hours.

Compared with the first time,

Water shortage: 48-32 =16km.

More current: 24- 16 = 8km.

So the downstream 16 km is the same as the upstream 8 km.

The downstream speed is 16÷8= twice the upstream speed.

It takes 48 kilometers to get along with water, and 48÷2=24 kilometers against the current.

The upstream speed is (24+16) ÷ 5 = 8km/h.

Downward speed is 8× 2 =16 km/h.

Still water speed: (8+ 16) ÷ 2 = 12km.

2.

The total number of students is a multiple of 5, and the unit of the total number is 5.

A multiple of three of the total number of boys,

The quotient of the total number of students divided by 5, odd number.

1×3=3

3×3=9, excluding

5×3=5, 5 repetitions, excluding.

7×3=2 1

9×3=27, excluding

The number of boys is a multiple of 3, so the sum of all the numbers is a multiple of 3.

Then try it separately

There are 3 boys, and there is no data that meets the requirements.

The number of boys is 1,

Boys: 26 1

Total: 26 1÷3×5=435

Meet the meaning of the question

So there are 435 people in this school.

3.

The sum of the numbers written by six people is: (87+92+98+99+104+10) ÷ 5 =118.

I don't understand what your topic means.

If you ask six children what is the closest sum of the numbers on the cards, it is 1 10.

4.

The remaining 52 cards, half red and half black, have 26 cards each.

The number of black in A is the same as the number of red in B..

Then the red in A and the black in B are the same.

Just look at a,

Black+Red =26 sheets

The red in A and the red in B add up to 26.

So the black in A is always equal to the red in B.

So the number of black cards in group A and red cards in group B will be exactly the same 1000 times.

5.

1= 1/2+ 1/2

= 1/2+ 1/3+ 1/6

The sum of the reciprocal of 2, 3 and 6 is equal to 1.