Elitmus
Exam
Numerical Ability
Arithmetic
Given a number N, 2*N has 28 factors and 3*N has 30 factors. Calculate how many factors will be there
in 6*N?
Read Solution (Total 8)
-
- he says 2*N has 28 factors - i considered N to be made of 2,3 prime factors.
Therefore 2*N = 2^6 * 3^3 (#note my original number N = 2^5 * 3^3)
only then the number of factors = (6+1) * (3+1)= 7 * 4= 28
now check for 2nd condition 3* N = 2^5 * 3^4 = (5+1)*(4+1)= 6*5=30
therfore my assumption was correct now u can find for 6* N = 2^6 * 3^4=(7)*(5) = 35 - 10 years agoHelpfull: Yes(16) No(1)
- 7*5=35
n=(3^6)(2^4) - 10 years agoHelpfull: Yes(8) No(1)
- Let
N=2^x * 3^y * 5^z * 7^a * 11^b *...
2*N= 2^(x+1) * 3^y * 5^z * 7^a * 11^b *... ,No. of factors= F1=(x+2) * (y+1) * (z+1) * (a+1) * (b+1) * ..
3*N= 2^x * 3^(y+1) * 5^z * 7^a * 11^b *..., No. of factors= F2=(x+1) * (y+2) * (z+1) * (a+1) * (b+1) * ..
now factorize 28 and 30
28=(2*2*7) or (4*7)
30=(2*3*5) or (6*5)
we see that both have maximum three factors. so we can write the numbers in this form
2*N= 2^(x+1) * 3^y * 5^z , and No. of factors= F1=(x+2) * (y+1) * (z+1)= 28 ----------(1)
3*N= 2^x * 3^(y+1) * 5^z , and No. of factors= F2=(x+1) * (y+2) * (z+1) = 30------------(2)
After this point we have to only check for which values of x,y, or z satisfy the both conditions. for this factorize anyone and put the values of x,y,z in the second equation.
now, F2=30 can factorized in (2*3*5) or (6*5)
case 1: F2= 2*3*5=(x+1) * (y+2) * (z+1)
so, x=1, y=1, z=4
now put the values of x,y,z in F1
F1= (x+2) * (y+1) * (z+1)=3*2*5=30 !=28,, this is not possible
case 2: F2= 6*5=(x+1) * (y+2)
so, x= 5, y=3
now put the values of x, y in F1
F1=(x+2) * (y+1) = (5+2)*(3+1)= 28.
now 6*N= 2*3* N= 2^(x+1) * 3^(y+1)= 2^6 * 3^4.
so no. of factors =(6+1)*(4+1)= 7*5= 35 - 10 years agoHelpfull: Yes(8) No(2)
- Can U explain how u got that answer??
- 10 years agoHelpfull: Yes(0) No(6)
- 2,3 are factors of 6
so
6*n has 28+30=58 factors - 10 years agoHelpfull: Yes(0) No(12)
- right ans is 42
take n=864 and check it - 10 years agoHelpfull: Yes(0) No(6)
- i think so the ans is 30
- 10 years agoHelpfull: Yes(0) No(5)
- N and 2^n gives 28 which means that there is no factor of 2 in n. So the number of factors is 30
- 9 years agoHelpfull: Yes(0) No(0)
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