Aptitude - Numbers - Discussion
Discussion Forum : Numbers - General Questions (Q.No. 40)
40.
(12345679 x 72) = ?
Answer: Option
Explanation:
| 12345679 x 72 | = 12345679 x (70 +2) |
| = 12345679 x 70 + 12345679 x 2 | |
| = 864197530 + 24691358 | |
| = 888888888 |
Discussion:
19 comments Page 1 of 2.
Satheeshkumar. D said:
1 decade ago
We can apply digit sum method:.
In digit sum method 9 and 0 considered the same.
Digit sum of 1234567 = 1 (1+2+3+4+5+6+7).
&.
Digit sum of 72 = 9 or 0 (7+2).
Now multiply this digit sums 1 x 0 = 0 or 9.
So the digit sum of the answer must be 0 or 9.
888888888 gives the answer of 0 or 9.
(8+8+8+8+8+8+8+8+8=72; 7+2=9).
(Tip: Whenever you count digit sum, skip the number 9 as if it is 0, it works and its true).
In digit sum method 9 and 0 considered the same.
Digit sum of 1234567 = 1 (1+2+3+4+5+6+7).
&.
Digit sum of 72 = 9 or 0 (7+2).
Now multiply this digit sums 1 x 0 = 0 or 9.
So the digit sum of the answer must be 0 or 9.
888888888 gives the answer of 0 or 9.
(8+8+8+8+8+8+8+8+8=72; 7+2=9).
(Tip: Whenever you count digit sum, skip the number 9 as if it is 0, it works and its true).
Ronit Singh said:
6 years ago
Why the hell you are applying these lengthy methods, just multiply last three digit i.e. 672 with 72 and you will see 8888 as the last 4 digit in the result and in option only A & B options are with 8888. So option B is the answer as when we multiply a 8 digit long number with two digit number then answer can not be in 8 digit long number. So answer is option B.
(4)
K.ARIVU SELVAN said:
9 years ago
12345679 * 72 = 12345679 * (63 + 9)
12345679 * 63 = 777 777 777 (+)
12345679 * 9 = 111 111 111
-------------------
12345679 * 72 = 888 888 888
I hope this will useful.
12345679 * 63 = 777 777 777 (+)
12345679 * 9 = 111 111 111
-------------------
12345679 * 72 = 888 888 888
I hope this will useful.
Priya said:
1 decade ago
@Satheeskumar.D
But how can we multiply this digit sum method by 1*0 or 0 or 9 as like as you mentioned above. That makes little bit tough. How is this? please explain.
But how can we multiply this digit sum method by 1*0 or 0 or 9 as like as you mentioned above. That makes little bit tough. How is this? please explain.
Daring Deep said:
9 years ago
One shortcut method is to check the divisibility of numbers by 9 since 72 is divisible by it.
In options, every no except answer is not divisible by 9.
In options, every no except answer is not divisible by 9.
(1)
Charan said:
1 decade ago
The best method is:
12345679*9=111 111 111
12345679*(72)=12345679*(9*8)=888 888 888
I hope this will help
12345679*9=111 111 111
12345679*(72)=12345679*(9*8)=888 888 888
I hope this will help
JAISON said:
8 years ago
12345679 x (70+2).
12345679 x 70 = 864197530,
12345679 x 2 = 24691358,
864197530 + 24691358 = 888888888.
12345679 x 70 = 864197530,
12345679 x 2 = 24691358,
864197530 + 24691358 = 888888888.
Kumar said:
7 years ago
12345679 * 72.
= 12345679*(9*8).
= 12345679*(10-1)*8.
= (123456790-12345679)*8.
= 11111111*8.
= 88888888.
= 12345679*(9*8).
= 12345679*(10-1)*8.
= (123456790-12345679)*8.
= 11111111*8.
= 88888888.
(9)
DeEpU said:
1 decade ago
12345679*72=12345679*(80-8)
8*12345679=98765432
987654320
- 98765432
------------
888888888
8*12345679=98765432
987654320
- 98765432
------------
888888888
Krishna said:
4 years ago
@Kumar
123456789 * 9 = 1111111101, then how do you get 111111111? Explain.
123456789 * 9 = 1111111101, then how do you get 111111111? Explain.
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