Question
Quantitative Aptitude Question on Number Systems
For any natural Number 'n', let an be the largest number not exceeding n , then a1 + a2 + a3... +a50 =
Let an be the largest integer not exceeding n.
We want to compute ∑n=150an.
We can find the values of an for n=1,…,50:
a1=1
a2=1
a3=1
a4=2
a5=2
a6=2
a7=2
a8=2
a9=3
...
a49=7
a50=7
We can group the terms as follows:
an=k if k2≤n<(k+1)2.
The number of times k appears in the sum is (k+1)2−k2=2k+1.
We want to find the largest integer k such that k2≤50.
72=49≤50 and 82=64>50.
Thus, the largest integer k is 7.
The values of an range from 1 to 7.
The number of times k appears in the sum is (k+1)2−k2=2k+1 for k=1,…,7.
The number of times 1 appears is 2(1)+1=3.
The number of times 2 appears is 2(2)+1=5.
The number of times 3 appears is 2(3)+1=7.
The number of times 4 appears is 2(4)+1=9.
The number of times 5 appears is 2(5)+1=11.
The number of times 6 appears is 2(6)+1=13.
The number of times 7 appears is 50−49+1=2.
The sum is:
∑n=150an=1(3)+2(5)+3(7)+4(9)+5(11)+6(13)+7(2)=3+10+21+36+55+78+14=217.
Final Answer: The final answer is 217
Solution
Let an be the largest integer not exceeding n.
We want to compute ∑n=150an.
We can find the values of an for n=1,…,50:
a1=1
a2=1
a3=1
a4=2
a5=2
a6=2
a7=2
a8=2
a9=3
...
a49=7
a50=7
We can group the terms as follows:
an=k if k2≤n<(k+1)2.
The number of times k appears in the sum is (k+1)2−k2=2k+1.
We want to find the largest integer k such that k2≤50.
72=49≤50 and 82=64>50.
Thus, the largest integer k is 7.
The values of an range from 1 to 7.
The number of times k appears in the sum is (k+1)2−k2=2k+1 for k=1,…,7.
The number of times 1 appears is 2(1)+1=3.
The number of times 2 appears is 2(2)+1=5.
The number of times 3 appears is 2(3)+1=7.
The number of times 4 appears is 2(4)+1=9.
The number of times 5 appears is 2(5)+1=11.
The number of times 6 appears is 2(6)+1=13.
The number of times 7 appears is 50−49+1=2.
The sum is:
∑n=150an=1(3)+2(5)+3(7)+4(9)+5(11)+6(13)+7(2)=3+10+21+36+55+78+14=217.
Final Answer: The final answer is 217