1. A man covered a certain distance at some speed. Had he moved 3 kmph faster, he would have taken 40 minutes less. If he had moved 2 kmph slower, he would have taken 40 minutes more. The distance (in km) is:
A. 35
B. 36[latex]\frac {1}{3}[/latex]
C. 37[latex]\frac {1}{2}[/latex]
D. 40
Answer: Option D
Explanation:
Let distance = x km and usual rate = y kmph.
Then, [latex]\frac {x}{y}[/latex] - [latex]\frac {x}{y+3}[/latex] = [latex]\frac {40}{60}[/latex] => 2y(y + 3) = 9x ....(i)
And,[latex]\frac {x}{y-2}[/latex] - [latex]\frac {x}{y}[/latex] = [latex]\frac {40}{60}[/latex] => y(y - 2) = 3x ....(ii)
On dividing (i) by (ii), we get: x = 40.
2. 18 men bind 900 books in 10 days. Find how many binders will be required to bind 600 books in 12 days?
Answer: Option A
Explanation:
We have to find the number of binders. Let the number of binders be x.
Direct Proportion:Less Books (↓),Less binders(↓)
Indirect Proportion:More days (↑),Less binders (↓)
\[ 18 : x ::
\begin{cases}
900 : 600 - - - (Books) \\
12 : 10 - - - (Days)
\end{cases}
\]
x × 900 × 12 = 18 × 600 × 10
x = [latex]\frac {18 \times 600 \times 10}{900 \times 12}[/latex] = 10
3. Find the value of [latex]^{20}c_{17}[/latex]
A. 1260
B. 1140
C. 2580
D. 3200
Answer: Option B
Explanation:
[latex]^nc_{r}[/latex] =[latex]\frac {^np_{r!}}{r!}[/latex]
[latex]^nc_{r}[/latex] = [latex]\frac {n!}{(r!) (n – r)!}[/latex]
[latex]^{20}c_{17}[/latex] =[latex]\frac {20!}{(17!) (20 – 17)!}[/latex]
[latex]^{20}c_{17}[/latex] =[latex]\frac {20 \times 19 \times 18 \times 17!}{(17!) (3)!}[/latex]
[latex]^{20}c_{17}[/latex] =[latex]\frac {20 \times 19 \times 18}{3 \times 2 \times 1}[/latex]
[latex]^{20}c_{17}[/latex] = 1140.
4. (1331)[latex]^{- (2/3)}[/latex]
A. –[latex]\frac {1}{11}[/latex]
B. – [latex]\frac {11}{121}[/latex]
C. [latex]\frac {1}{122}[/latex]
D. [latex]\frac {121}{11}[/latex]
Answer: Option C
Explanation:
Cube root of 1331 is 11. Therefore,
(11)[latex]^{3 \times -(2/3)}[/latex]
Remember the law of indices (xm)n = xmn
(11)[latex]^{3 \times -(2/3)}[/latex] = 11[latex]^{-2}[/latex]
x[latex]^{-1}[/latex] = [latex]\frac {1}{x}[/latex]
Hence, 11[latex]^{-2}[/latex] = [latex]\frac {1}{112}[/latex] = [latex]\frac {1}{112}[/latex]
5. Two pipes can fill a tank in 8 hrs & 6 hrs respectively. If they are opened on alternate hours and if pipe A gets opened first, then in how many hours, the tank will be full?
A. 6 hrs
B. 7 hrs
C. 8 hrs
D. 14 hrs
Answer: Option B
Explanation:
Pipe A's work in 1 hr = [latex]\frac {1}{8}[/latex]
Pipe B's work in 1 hr = [latex]\frac {1}{6}[/latex]
Pipes (A+B)'s work in first 2 hrs when they are opened alternately = 1/8 + 1/6 = 7 /24
Now,
In 4 hrs they fill : 2 X ([latex]\frac {7}{24}[/latex]) = [latex]\frac {7}{12}[/latex]
In 6 hrs they fill : 3 X ([latex]\frac {7}{24}[/latex]) = [latex]\frac {7}{8}[/latex]
After 6 hrs, part left empty = [latex]\frac {1}{8}[/latex]
Now it is A's turn to open up.
In one hr it fills [latex]\frac {1}{8}[/latex] of the tank.
So, the tank will be full in = 6 hrs + 1 hr = 7 hrs.