Which chemical is required for removing, $MgS{O}_4$ from the raw-water?

A club collected exactly USD 599 from its members. If each member contributed at least USD 12, what is the greatest number of members the club could have?

When a number is divided by 7, the remainder is 3. What will be the remainder when twice the number plus 5 is divided by 7?

A two-digit number is 4 times the sum of its digits. When the digits are reversed, the new number is 18 greater than the original number. What is the original number?

A candidate answers a multiple-choice question by guessing. There are 4 choices. The probability of answering correctly is:

If a sum of Tk. 1,000 is invested at an annual compound interest rate of 10%, compounded once a year, what will be the compound interest earned after 2 years?

The average (arithmetic mean) of 8 numbers is 20. If one of the numbers, 32, is excluded from the set, what will be the average of the remaining 7 numbers?