1) When the bus No.677 arrives at Wangjing Hospital, 2/5 passengers get off and 2 1 people get on. At this time, there were 30% more passengers on board. How many people are there in the car? (Detailed process is required)

Assuming there are X people in the car, there are: X * (1-2/5)+21= X * (1+30%).

X=30

2) My mother bought 4,000 yuan of national construction bonds last year with a fixed term of five years, with an annual interest rate of 2.63% and interest tax of 20%. How much interest can my mother get back when it expires? Is this 420.8 yuan or more than 500 yuan? Please know the detailed process. )

=4000+4000*2.63%*5*( 1-20%)=4420.80

3) Only the formula does not count. A rope is 60% used, leaving 12 meters. How long is this rope?

= 12/( 1-60%)=30 (m)

4) Xiao Gan lives on the sixth floor of the 15 floor below. The height from his floor to the ground measured during construction is 10 meter. How high is this building? Is the floor on the sixth floor the height of the base from the ground?

Building height =10/(6-1) *15 = 30m.

The floor on the sixth floor is five floors above the ground.