Problem Solving

Question:

What is the unit digit of 1007*1034*1221*15343*100009*10034*1091*1191*1233?

a. 6
b. 0
c. 4
d. 2
e. 8

Finding answer to this question should not take more than 15-20 secs. If you spend more than half a min than you need to check out the idea behind this question. Solution with the shortcut will be posted after 24 hrs time.

Thanks,
Quant-Master

Answer is D.

Good question. But can we stop doing the 'solution will be posted after discussion' or 'after 24 hours'. It takes away from the what people are looking for on this site which is to solve the question, confirm the answer or learn from others the best approach to solve the question.

Thanks.

Answer is D - 2. You multiply only the units digits, and each time drop all other numbers except the units digit.

D-2
In general- last n digits of any multiplication depend upon the multiplication of the last n digits of all the numbers.
here n happens to be 1.

quant-master wrote:Question:

What is the unit digit of 1007*1034*1221*15343*100009*10034*1091*1191*1233?

a. 6
b. 0
c. 4
d. 2
e. 8

Finding answer to this question should not take more than 15-20 secs. If you spend more than half a min than you need to check out the idea behind this question. Solution with the shortcut will be posted after 24 hrs time.

Thanks,
Quant-Master

OA is D

Like mentioned by other users above, the idea is to multiply only the unit digits of each number.

1007*1034*1221*15343*100009*10034*1091*1191*1233

multiply 7*4 =28 (forget 2, take only 8)
multiply 8*3= 24 (I ignored the 3rd number as unit digit of that number is 1 and 1 multiplied by any number is that number)
multiply 4*9 = 36
multiply 6*4 = 24
multiply 4*3 =12 (I ignored 1 again). Hence unit digit is 2

Let me know if you have any queries.

Thanks,
Quant-Master