Aptitude - Number
1.
The unit digit in 7105 is :
Answer
Answer :
Option BExplanation :
Unit digit of (7)4 = 1. Now, 7105 = (74)26 x 7
∴ Unit digit in (74)26 = 1.
So, unit digit in (74)26 x 7 is (1 x 7) = 7
2.
If 17200 is divided by 18, the remainder is :
Answer
(xn − an) is divisible by (x + a) for even values of n.
(17200 − 1200) is divisible by (17 + 1)
(17200 − 1) is divisible by 18
When 17200 is divided by 18, the remainder is 1.
Answer :
Option CExplanation :
(xn − an) is divisible by (x + a) for even values of n.
(17200 − 1200) is divisible by (17 + 1)
(17200 − 1) is divisible by 18
When 17200 is divided by 18, the remainder is 1.
3.
1014 x 986 =
Answer
(a + b)(a − b) = a2 − b2
1014 x 986 = (1000 + 14) x (1000 − 14) = 10002 − 142
10,00,000 − 196 = 999804
Answer :
Option DExplanation :
(a + b)(a − b) = a2 − b2
1014 x 986 = (1000 + 14) x (1000 − 14) = 10002 − 142
10,00,000 − 196 = 999804
4.
6894 x 99 =
Answer
6894 x 99 = 6894 x (100 − 1)
= 6894 x 100 − 6894 x 1
= 689400 − 6894 = 682506
Answer :
Option CExplanation :
6894 x 99 = 6894 x (100 − 1)
= 6894 x 100 − 6894 x 1
= 689400 − 6894 = 682506
5.
(64)2 − (36)2 = 20 x p, then p = ?
Answer
(64)2 − (36)2 = (64 + 36)(64 − 36) = 100 x 28 = 2800
20 x p = 2800 ;
∴ p = 140
Answer :
Option DExplanation :
(64)2 − (36)2 = (64 + 36)(64 − 36) = 100 x 28 = 2800
20 x p = 2800 ;
∴ p = 140
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