Thirty percent of the members of a swimming club have passed lifesaving test. Among the members who have not passed the test, 12 have taken the preparatory course and 30 have not.

A box contains only marbles. If ¼ the marbles were removed, the box would be filled to 1/3 of its capacity. If instead 100 marbles were added, the box would be full. How many marbles are there in the box?

Minhaz and Alam can complete a work in 18 days . After working together for 12 days Minhaz stops and Alam competes the remaining work in 8 days. In how many days can Minhaz complete the work if he works alone?

In a mixture A is 20%, B is 20% and rest is C. If 250ml water is mixed with 750ml mixture, then what will be the ratio of water and C?

ABCD is a parallelogram such that AB is parallel to DC and DA parallel to CB. The length of side AB is 20cm. E is a point between A and B such that the length of AE is 3cm. F is a point between points D and C. Find the length of DF such that the segment EF divide the parallelogram in two regions with equal areas.