Several math problems (application problems) in the first grade of junior high school

1, the speed is increased by 50%, that is, the speed is 1.5 times of the original speed.

So the time is11.5 = 2/3, which is less than the original time 1-2/3= 1/3.

Therefore, the original time =20÷ 1/3=60 minutes = 1 hour.

Distance =4× 1=4 km

The average speed of vehicles has increased by 30 kilometers per hour.

Then the original speed of four hours is 30× 4 = 120km less than now.

Add 30 kilometers, and it will take 7-4=3 hours to walk at the original speed.

Therefore, the original speed = (120+30) ÷ (7-4) = 50km/h.

Distance = 50× 7 = 350km

3. Reading and homework * * * takes 25+35=60 minutes.

Doing homework takes twice as long as reading.

That is, the whole time is divided into three parts: reading time 1 part and homework time.

Therefore, the reading time =60× 1/3=20 minutes.

You should dial 25-20=5 minutes.

4. Illegal income = 270010 = 270 yuan/Taiwan.

If the original price is X, the selling price is x×( 1+40%)×0.8, and the income is X × (1+40%) × 0.8-X.

That is, x×( 1+40%)×0.8-x=270.

Solution, x=2250 (yuan)