Find the greatest number of four digits which when divided by $10, 15, 21$ and $28$ leaves $4, 9, 15$ and $22$ as remainders,respectively.

$HCF$ of $4 \times 27 \times 3125$,$8 \times 9 \times 25 \times 7$ and $16 \times 81 \times 5 \times 11 \times 49$ is

Seema,Meena,and Reena start jogging around a circular stadium and complete one round in $54 \text{ seconds}$,$42 \text{ seconds}$,and $63 \text{ seconds}$ respectively. Approximately after how many minutes will they meet again at the starting point?

In a school,$391$ boys and $323$ girls have been divided into the largest possible equal classes,so that each class of boys numbers the same as each class of girls. What is the number of classes?

The $HCF$ and $LCM$ of two numbers are $21$ and $84$ respectively. If the ratio of the two numbers is $1:4$,then the larger of the two numbers is

$H.C.F.$ of $\frac{2}{3}, \frac{4}{5}$ and $\frac{6}{7}$ is