What is the ratio of the simple interest earned on a certain amount at the rate of 21% per annum for 8 years to that earned on the same sum at the same rate for 21 years?  

The cost of 3 kg of rice is ₹180. The cost of 8 kg of rice is equal to that of 5 kg of pulse. The cost of 15 kg of pulses is equal to that of 2 kg of tea. The cost of 3 kg of tea is equal to that of 6 kg of walnuts. What is the cost (in ₹) of 10 kg of walnuts? 

What is the compound interest on a sum of ₹25,000 after three years at a rate of 12 per cent per annum interest compounded yearly?  

A boat covers 35 km downstream in 2 h and covers the same distance upstream in 7 h. Find the speed (in km/h) of the boat in still water.  

What is the difference (in ₹) between the simple interest and the compound interest on a sum of ₹8000 for $$32{2\over 5}$$ years at the rate of 10% p.a., when the interest is compounded yearly?

$$ if \ {1\over x}+x=4,$$ then find $${1\over x^2}+x^2$$

The mode of the following data is __________.

13,15,31,12,27,13,27,30,27,28 and16

The number 1254216 is divisible by which of the following numbers?