In a 4-digit number, the sum of the first two digits is equal to that of last two digits. The sum of the first and last digits is equal to third digit. Finally, the sum of the second and fourth digits is twice the sum of the other two digits. What is the third digit of the number?
A. 5
B. 8
C. 1
D. 4
Answer: Option A
Solution(By Examveda Team)
Let the 1st, 2nd, 3rd and 4th digits be a, b, c and d respectively. Then, a + b = c + d ----------(i) a + d = c ----------(ii ) b + d = 2(a + c) ----------(iii) from eqn. (i) and (ii), a + b = a + 2d →b = 2d and eqn (iii); 2d + d = 2(a + a + d)→ 3d = 2(2a + d) → d = 4a or, a = $$\frac{{\text{d}}}{4};$$
→ Now, from eqn. (ii),
a + d = $$\frac{{\text{d}}}{4}$$ + d = $$\frac{{{\text{5d}}}}{4}$$ = c Or, c = $$\frac{5}{{4{\text{d}}}}$$ The value of d can be either 4 or 8. If d = 4, then c = 5 If d = 8, then c = 10 But the value of c should be less than 10 Hence, value of c would be 5
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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
Why is the value of d either 4 or 8?