Two workers paint doors on a house in 2 days together. The first person works in 4 days then take a break while the second person continues to paint in 1 then they finish. How many days does each worker need to finish the job working seperately?

Calculate:

$\left( 1-\frac{3}{4} \right)\times \left( 1-\frac{3}{7} \right)\times \left( 1-\frac{3}{10} \right)\times \left( 1-\frac{3}{13} \right)\times ......\times \left( 1-\frac{3}{97} \right)\times \left( 1-\frac{3}{100} \right)$

A piece of pasture grows at a constant rate every week.

120 cows will eat up the grass in 12 weeks.

150 cows will eat up the glass in 8 weeks.

How many cows can the pasture sustain for 6 weeks ?

A bookshelf had 3 levels and a total of 240 books. The same number of books are the 2^nd level were shuffled from the 1^st level to the 2^nd level. The same number of books as the 3^rd level were then shuffled from the 2^nd to the 3^rd level. Finally, the same number of books as the remaining books on the 1^st level wwere shuffled from 3^rd to the 1^st level.

The ratio of the number of books on the 3 levels became 1 : 2 : 3. How many books were on each level at first ?

Calculate:

$\frac{1313}{2121}\times \frac{165165}{143143}\times \frac{424242}{151515}$ ?

It is now 17 minutes to 3. After how long will the hour and minute hand overlap?

A boy goes into a shop to buy black and blue pens. The amount of money to buy 3 black pens is more than the money to buy blue pens. The money to buy 2 blue pens is more than the money to buy 5 black pens. How much does each pen cost in both colour? ( Know the cost of a pencil of each type does not exceed 1000 VND and is a hundred dollars )

Calculate the sum of numbers needed to write the dates on year 2012 calendar. Knowing that in 2012, there are 7 months of 31 days, and 2 months of 29 days.

Arrange some cubes with each edge of 1cm into a bigger cube with the volume of 125cm^3.  . After that, paint on all faces of the bigger cube. How many smaller cubes are painted none? 

Find the two numbers know that their sum is 546, if  the big number is no change and  the small number increases by three times, the big number is twice the new number.

A figure is give:

Knowing that ABCD and DEGH are squares. The perimeter of ABCD and DEGH are 80cm and 64cm in order. Calculate the triangle BEH.

Find the area of the rectangle has the perimeter is 240m. If the length increases by 5m and the width decreases by 5m, then the area will also decreases by 175${{m}^{2}}$  .

If the length is no change  and the width is decreases by 5m, the original area of the rectangle is decreases by 5 times the length.

If the width is no change and the length is increases by 5m, the area is increases by 5 times the width.

A rectangular field has the perimeter is 180m. If the width is increases by 8m, the length is decreases by 8m, find the area of the rectangle?

A store sells 138 liters of oil in two days, if the first day the store sells 12 liters more than the reality and the second day, the store sells 25 liters less than the reality, the second day sells by $\frac{1}{4}$ the first day. How many liters of oil did the store sell every day?

Mai bought 10 notebooks, Lan bought 12 notebooks. The number of Dao’s notebooks is equal to the average of Mai and Lan. Cuc bought 3 notebooks more than the average of Mai, Lan and Dao. How many notebooks did Cuc buy?