If 31z5 is a multiple of 9, where z is a digit, what is the value of z? You will find that there are two answers for the last problem. Why is this so?

If 21y5 is a multiple of 9, where y is digit, what is the value of y?

If 24x is a multiple of 3, where x is a digit what is the value of x?

What is Z-scheme in light reaction of photosynthesis? Why is it called so?

Find the distance of the point (3,4,-5) from Z-axis.

Find 4x xx 5y xx 7z . First find 4x xx 5y and multiply it by 7z or first find 5y xx 7z and multiply it by 4x: Is the result the same? What do you observe? Does the order in which you carry out the multiplication matter?

What are the intercepts made by the plane 3x - 6y + z = 9 with the coordinate axes ?

A man of mass 70 kg stands on a weighing scale in a lift which is moving (a) upwards with a uniform speed of 10 m s^1 (b) downwards with a uniform acceleration of 5 m s^2, upwards with a uniform acceleration of 5 m s-^1z. What would be the readings on the scale in each case? What would be the reading if the lift mechanism failed and it hurtled down freely under gravity?

A man walks on a straight road from his home to a market 2.5 km away with a speed of 5 km h ^-1 . Finding the market closed, he instantly turns and walks back home with a speed of 7.5 km h^-1 . What is the average speed of the man over the interval of time (i) 0 to 30 min, (ii) 0 to 50 min, (Hi) 0 to 40. min? [Note: You will appreciate from this exercise why . it is better to define average speed as total path length divided by time, and not as magnitude of average velocity. You would not like to tell the tired man on his return home that his average speed was zero!]