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Aptitude - Numbers

Exercise : Numbers - General Questions
121.
What is the unit digit in the product (365 x 659 x 771)?
1
2
4
6
Answer: Option
Explanation:

Unit digit in 34 = 1 Unit digit in (34)16 = 1

Unit digit in 365 = Unit digit in [ (34)16 x 3 ] = (1 x 3) = 3

Unit digit in 659 = 6

Unit digit in 74 Unit digit in (74)17 is 1.

Unit digit in 771 = Unit digit in [(74)17 x 73] = (1 x 3) = 3

Required digit = Unit digit in (3 x 6 x 3) = 4.

122.
3251 + 587 + 369 - ? = 3007
1250
1300
1375
1200
None of these
Answer: Option
Explanation:
 3251          Let 4207 - x = 3007
+ 587          Then,  x = 4207 - 3007 = 1200
+ 369
 ----
 4207
 ----
123.
7589 - ? = 3434
4242
4155
1123
11023
None of these
Answer: Option
Explanation:

Let 7589 -x = 3434

Then, x = 7589 - 3434 = 4155

124.
217 x 217 + 183 x 183 = ?
79698
80578
80698
81268
Answer: Option
Explanation:
(217)2 + (183)2 = (200 + 17)2 + (200 - 17)2
= 2 x [(200)2 + (17)2]       [Ref: (a + b)2 + (a - b)2 = 2(a2 + b2)]
= 2[40000 + 289]
= 2 x 40289
= 80578.
125.
The unit digit in the product (784 x 618 x 917 x 463) is:
2
3
4
5
Answer: Option
Explanation:
Unit digit in the given product = Unit digit in (4 x 8 x 7 x 3) = (672) = 2
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