Here are some solved questions from Infosys  Placement Papers

1) If one-seventh of a number exceeds its eleventh part by 100 then the number is…

(i) 770
(ii) 1100
(iii) 1825
(iv) 1925

Solution:

Let the number be x. Then X/7 - x/11 =100 11x-7x = 7700 x=1925.

2) The ratio of Rita's age to her mother's age is 3:8. The difference of their ages is 35 years. The ratio of their ages after 4 years will be:

(i) 7:12
(ii) 5:12
(iii) 38:43
(iv) 42:47

Solution:
Let their ages be 3x and 8x
8x - 3x =35
x =7
Their present ages are 21 and 56 years.
Ratio of their ages after 4 years are 25:60 = 5:12

3) Gold is 19 times as heavy as water and copper is 9 times as heavy as water. In what ratio should these be mixed to get an alloy 15 times as heavy as water?

(i) 1:1
(ii) 2:3
(iii) 1:2
(iv) 3:2

Solution:
Let 1gm of gold be mixed with x gm of copper to give (1+x)gm of the alloy.
1G=19W, 1C = 9W and alloy = 15W 1gm gold + x

4) A tap can fill the tank in 15 minutes and another can empty it in 8 minutes. If the tank is already half full and both the taps are opened together, the tank will be:

(i) filled in 12 min
(ii) emptied in 12 min
(iii) filled in 8 min
(iv) emptied in 8 min

Solution:
Rate of waste pipe being more the tank will be emptied when both taps are opened.
Net emptying workdone in 1min =(1/8 -1/16)= 1/16
So full tank will be emptied in 16 min
Half tank will be emptied in 8 minutes.