A cloth merchant buys cloth from a weaver and cheats him by using a scale which is 10 cm longer than a normal metre scale. He claims to sell cloth at the cost price to his customers, but while selling uses a scale which is 10 cm shorter than a normal metre scale. What is his gain

In a gathering of 100 people, 70 of them can speak Hindi, 60 can speak English and 30 can speak French. Further, 30 of them can speak both Hindi and English, 20 can speak both Hindi and French. If x is the number of people who can speak both English and French, then which one of the following is correct? (Assume that everyone can speak at least one of the three languages.)

A person goes to a market between 4 p.m. and 5 p.m. When he comes back, he finds that the hour hand and the minute hand of the clock have interchanged their positions. For how much time (approximately) was he out of his house

There are three brothers. The sums of ages of two of them at a time are 4 years, 6 years and 8 years. The age difference between the eldest and the youngest is

Consider the following in respect of natural numbers a, b and c :

1. LCM (ab, ac) =a LCM( b, c)
2. HCF (ab, ac) = a HCF (b, c)
3. HCF (a, b) < LCM (a, b)
4. HCF (a, b) divides LCM (a,b).

Which of the above are correct

The value of k, for which the system of equations 3x-ky-20=0 and 6x-10y+40 = 0 has no solution, is