The weights of 4 boxes are 30, 40, 50 and 80 kilograms. Which of the following cannot be the total weight, in kilograms, of any combination of these boxes and in a combination a box can be used only once?

If "–" stands for division, "+" stands for multiplication, "÷" stands for subtraction and "×" stands for addition, which of the following equations is correct?

In the following questions, correct the equation by interchanging two signs.
9 × 3 + 8 ÷ 4 – 7= 28

If ‘+’ stands for division, ÷ stands for multiplication, multiplication stands for addition; then which one of the following equation is correct?

In a school, the bell is rung once after each half an hour. The school starts at 8:00 a.m. and closes at 1: 30 p.m. The bell is rung 3 times continuously, at the time of beginning, at the time of lunch break at 10:00 and 10:30 a.m. and at the end. How many times is the bell rung every day? 

Ashok's mother was 3 times as old as Ashok 5 years ago. After 5 years she will be twice as old as Ashok. How old is Ashok today? 

If ‘P’ means ‘÷’ and ‘Q’ means ‘+’ and ‘R’ means ‘×’ then Find the value of 16 P 8 Q 9 R 12?