Quantitative Aptitude - Arithmetic Ability Questions

7 does not occur in 1000. So we have to count the number of times it appears between 1 and 999. Any number between 1 and 999 can be expressed in the form of xyz where 0 < x, y, z < 9.

1. The numbers in which 7 occurs only once. e.g 7, 17, 78, 217, 743 etc

This means that 7 is one of the digits and the remaining two digits will be any of the other 9 digits (i.e 0 to 9 with the exception of 7)

You have 1*9*9 = 81 such numbers. However, 7 could appear as the first or the second or the third digit. Therefore, there will be 3*81 = 243 numbers (1-digit, 2-digits and 3- digits) in which 7 will appear only once.

In each of these numbers, 7 is written once. Therefore, 243 times.

2. The numbers in which 7 will appear twice. e.g 772 or 377 or 747 or 77

In these numbers, one of the digits is not 7 and it can be any of the 9 digits ( 0 to 9 with the exception of 7).

There will be 9 such numbers. However, this digit which is not 7 can appear in the first or second or the third place. So there are 3 * 9 = 27 such numbers.

In each of these 27 numbers, the digit 7 is written twice. Therefore, 7 is written 54 times.

3. The number in which 7 appears thrice - 777 - 1 number. 7 is written thrice in it.

Therefore, the total number of times the digit 7 is written between 1 and 999 is

243 + 54 + 3 = 300

Given exp . is like this 854*854*854-276*276*276854*854+854*276+276*276=?

so ans = 854 - 276 = 578

Given year, 2013 when divided by 4 leaves a remainder of 1.

NOTE: When the remainder is 1, 11 is substracted from the given year to get the result.

So, 2013 - 11 =2002

Raghu can complete the work in (12 x 9)hrs = 108 hrs.

 Arun can complete the work in (8 x 11)hrs = 88 hrs.

Raghu's 1 hrs work = 1/108 and Arun's 1 hrs work = 1/88

(Raghu + Arun)'s 1 hrs work = 1108+188=492376

 
So, both Raghu and Arun will finish the work in 237649 hrs

Number of days of 12 hours each=237649×112 = 19849=4349 days

Total numbers = 25

 Numbers divisible by 4 or 7 are 4, 7, 8, 12, 14, 16, 20, 21, 24 = 9

 The probability (divisible by 4 or 7) = 9/25

43 x 616.6/100 + 37 x 217/100

=> 265.138 + 80.29

=>  345.428

By investing Rs. 136, income obtained = Rs. 10.

By investing Rs. 6800, income obtained = Rs.1036×6800 = Rs. 500.