Q21. 
A number of three digits in base 7, when expressed in base 9, has its digits reversed in the order. What is the sum of the digits of the number? 
A.  5 

B.  6 

C.  7 

D.  8 
Q22. 
When the index of an exponential expression with a positive base is doubled, then the expression increases by $700%$. If one of the values that the base cannot have is $X$ which of the following is not a possible value of $P$? 
A.  4 

B.  8 

C.  5 

D.  1 
Q24. 
The mean salary in ICM ltd. was Rs 1500, and the standard deviation was Rs 400. A year later each employee got a Rs 100 raise. After another year each employee's salary (including the above mentioned raise) was increased by $20%$. The standard deviation of the current salary is: 
A.  460 

B.  480 

C.  560 

D.  none of these 
Q25. 
Three persons Suresh, Devesh and Prashant were born on different days in the same year. If the date and month of birth of Suresh, Devesh and Prashant are numerically equal, then what could be the minimum difference in the ages of youngest and oldest in days? 
A.  56 

B.  60 

C.  61 

D.  62 