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?

The average of three numbers is 369. Find that three numbers, knowning that three numbers have: a 3 - digit number; a 2 – digit number and a 1 – digit number?

In a working day, the four groups planted 174 eucalyptus trees. Group 1 planted 16 trees more than group 2, group 3 planted 10 trees less than group 1, group 4 planted is equal to the number of trees group 2. How many eucalyptus trees did each group plant?

Average age of father, An and Hong is 19 years old, the father's age is 25 years more than the total age of An and Hong, Hong is 8 years less than An. How old is each person?

An is 12 years younger than Binh. In 1997, An’s age is $\frac{3}{7}$ Binh’s age. What is the age of An in 2000?

A few years ago, there are four Mondays and four Fridays in the month of January. On which day in that year was 1^st of January ?

The sum of a father’s age and his son’s age is 60. The father’s age was 3 times his son’s age eight years ago. How old are they now ?

Find the smallest natural number N consist of 9 digits is $N=\overline{abceghik}$ , such that $\overline{ab}\vdots 2;\overline{abc}\vdots 3;\overline{abc\text{d}}\vdots 4;\overline{abc\text{d}e}\vdots 5;\overline{abc\deg }\vdots 6;\overline{abc\deg h}\vdots 7;\overline{abc\deg hi}\vdots 8;N\vdots 9$?

A rectangular piece of land has the length is 64m and the width is 34m. They decrease by the length and increase by the width so that the piece of land is square, knowing that the area decreases to the length of 272 m² . Find the area more follow the width ? (m² )

Randy and Sam spend 12 hours to complete a science project. If Randy works alone on the same project for 16 hours and let Sam take over, Sam needs another 7 hours to complete it. How many hours does Sam spend to complete the science project alone ?

A number is added to 3. The sum is then multiplied by 5. When 8 is subtracted from the product, the result is 12. Find the number at first ?

The ratio of the number of yellow balls to the toal number of balls in a bag was 5:7 at first. 18 more yellow balls were put into the bag. The ratio of the number of yellow balls to the total number of balls became 2 : 1. How many balls were there altogether in the end ?