How many even 4 – digit numbers such that hundreds digit is 2 that can be formed by using the digits: 0; 1; 2; 3; 4 ?

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 ? 

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:

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