What is the least number of soldiers that can be drawn up in troops of 12, 15, 18 and 20 soldiers and also in form of a solid square?
A. 900
B. 400
C. 1600
D. 2500
Answer: Option A
Solution(By Examveda Team)
In this type of question, We need to find out the LCM of the given numbers. LCM of 12, 15, 18 and 20; $$\eqalign{ & 12 = 2 \times 2 \times 3; \cr & 15 = 3 \times 5; \cr & 18 = 2 \times 3 \times 3; \cr & 20 = 2 \times 2 \times 5; \cr} $$Hence, LCM = $$2 \times 2 \times 3 \times 5 \times 3$$ Since, the soldiers are in the form of a solid square. Hence, LCM must be a perfect square. To make the LCM a perfect square, We have to multiply it by 5,
hence,
The required number of soldiers
= $$2 \times 2 \times 3 \times 3 \times 5 \times 5$$
= 900
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Comments ( 7 )
Related Questions on Number System
Three numbers are in ratio 1 : 2 : 3 and HCF is 12. The numbers are:
A. 12, 24, 36
B. 11, 22, 33
C. 12, 24, 32
D. 5, 10, 15
5 is multiplied because in the LCM(2×2×3×3×5), 2and 3 are in pairs while 5 is single and for complete square we have to make its pair also. So another 5 is multiplied.
How do we know that we need to multiply by 5 to get a perfect square
LCM is multiply by 5 because 180*5=900 which is a perfect square... another example if LCM is 60 we have to multiply it with 6 to get a perfect square 360..
@Mohd Amjad
To make a perfect square.
Why 5 is multiplied to make it a perfect square.?
Please put logit , why LCM multiply by 5 ?
why lcm multiply by 5 ?