In a ΔPQR, S and T are mid–points of the
sides PQ and PR respectively. U is a point
on ST such that SU: UT = 2 : 5. If SU = 8,
then the length of QR is–

60 men working 12hr a days complete a
work in 30 days
1 Man work in 1 hr a day complete a work in
= 30 × 60 × 12 = 21600 days
∴ 90 men working 8hr a day can complete
the same work in =
$21600\over90x8$
= 30 days

The ratio between boys and girls in a school
is 6 : 8 respectively. If the number of boys is
increased by 200 the ratio becomes 7 : 8
respectively. How many girls are there in
the school?

The average of 6 quantities is 10.
Therefore, the sum of all 6 quantities is 60.
The average of 4 of them is 8.
Therefore the sum of 4 quantities = 32
Therefore, the sum of the
remaining two quantities = (60 – 32) = 28
Hence the sum average of the 2 qunatities
= $28\over2$= 14