Given the two numbers $\overline{ab}$ and $\overline{ba}$ ( a > b ). Know the sum of them is a number that its the ones digits is 3 and the difference of them is a number such that its the ones digits is 7. Find a and b ? 

Find the sum of all the 3 – digit numbers, each number is divisible by 5 and its three digits are odd number ?

Given the two numbers $\overline{ab}$ and $\overline{ba}$ ( a > b ). Know the sum of them is a number that its the ones digits is 3 and the difference of them is a number such that its the ones digits is 7. Find a and b ?

A person sold totally the number of ducks in a day. In the morning, selling $\frac{2}{5}$of the number of ducks. In the evening, selling $\frac{3}{4}$of the number of remaining ducks. At night, selling 6 ducks and it is out of ducks. How many ducks did that person sell ?

Calculate quickly : $\frac{1}{2}\times \frac{1}{3}+\frac{1}{3}\times \frac{1}{4}+\frac{1}{4}\times \frac{1}{5}+\frac{1}{5}\times \frac{1}{6}$

( Write the result as a/b )

Lan’s mother has 90kg rice. Lan’s mother sells 1/5 of the amount of rice in the morning . To sell $\frac{1}{6}$ of the amount of remaining rice. How many part of the amount of rice at first did Lan’s mother sell ? ( Write the result as a/b )

There are 15 worker to do a job together. They will complete the job in 20 days. After doing in 8 days together, 5 more workers are added to the team to do the job. How many days do all workers continue to complete the job together ?

Nam and Bac make a tool together . Nam makes in 5 hours and Bac makes in 4 hours, Nam will make 13 tools more than Bac. Such that , if making in the same time is 8 hours, Nam is 24 tools less than Bac. How many tools does each person make in 1 hour ?

An spends 65000vnd to  buy two soap boxes and 1 meter material. Binh spends 95000cnd to buy one soap box and 1 meter silk. Such that the price of 1 meter silk is 3 times the price of 1 meter material. Find the price of one soap box ?

Ha, Nam, Ninh buy label together. Such that Ha and Nam buy 27 labels, Nam and Ninh buy 30 labels . Ninh and Ha buy 33 labels. How many labels does each person buy ?

Find fraction $\frac{a}{b}$ such that :

$\frac{1}{4}-\frac{2}{5}+\frac{a}{b}=\frac{1}{10}$  ( Write the result as a/b )

Calculate : $$ $(1-\frac{1}{5})\times \left( 1-\frac{1}{6} \right)\times \left( 1-\frac{1}{7} \right)\times \left( 1-\frac{1}{8} \right)\times \left( 1-\frac{1}{9} \right)$

( Write the result as a/b )

Calculate:

$A=\frac{38}{25}+\frac{9}{10}-\frac{11}{15}+\frac{13}{21}-\frac{15}{28}+\frac{17}{36}-...+\frac{197}{4851}-\frac{199}{4950}$ ?

An group of workers fix a road in 2 days. In the first day, they fix half of the road and 36m. The distance of road fixed in the first day is double the second day. How many metres of road is fixed in 2 days?

The sum of current age of and a brother and his younger sister is 24. When the brother’s age is equal to his sister’s current age, then his age is 3 times the sister’s age. How old is each person now?