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Where are the test papers from Kaifeng primary school to junior high school?
(1)0, 1+2+3+4+5= 15, which means that 5 digits can be divisible by 3, so a prime number cannot be formed.

(2) 9,92 bits are 1, 9 3 bits are 9, 9 4 bits are 1, ... twice a cycle,

So bit 89 102 is 1,

7, 7 2 is 9, 7 3 is 3, 7 4 is 1, 7 5 is 7, 7 6 is 9, ...

Four times in a cycle

So 27, 63 is 3.

Answer: 4

(3)s=vt Because the speed is constant, time is proportional to the distance. So the distance ratio from the front to the rear is 3: 8.

If the length of the bus is x meters, then

x:(3 15+x)=3:8

X= 189。

The length of the bus is 189 meters.

(4) 10÷ (father speed-son speed) × father speed = distance for father to catch up with his son.

therefore

Distance traveled by father to catch up with son = 10÷( 1- speed of son ÷ speed of father)

Dad can take three steps, but his son can take five.

The distance that the father takes 9 steps is equal to the distance that the son takes 17 steps.

Dad takes nine steps, three or three steps.

The time for my son to take 17 steps is 17÷5 5 steps.

The distance that the father takes 9 steps is equal to the distance that the son takes 17 steps.

Dad takes three steps as long as his son takes five.

So the speed of the son/the speed of the father = 3/(17/5) =15/17.

therefore

The distance a father walks behind his son =10 ÷ (1-15/17) = 85 meters.

Note: what I wrote is all about solving problems, so I need to sort it out myself!