Chain Rule Questions Answers

1. If 16 toys cost 240, then what do 40 toys cost ?
 Rs. 600
 Rs. 620
 Rs. 640
 Rs. 660
Answer And Explanation
Answer: Option C
Explanation:
Although we can first calculate the cost of one toy and then can multiply it with 40 to get the result.
but we will solve it with chain rule so that we can prepare ourself for other complex problems which we can solve easily by applying this rule.
Let the required cost be Rs. x
More toys means More Cost. (Direct Proportion)
\begin{aligned}
15:40 :: 240:x \\
=> x = \frac{240*40}{15} \\
=> x = 640
\end{aligned}
So 40 toys will cost Rs 640 
2. If the cost of x metres of wire is d rupees, then what is the cost of y metres of wire at the same rate ?
 xd
 yd
 yd/x
 x/yd
Answer And Explanation
Answer: Option C
Explanation:

3. If the price of 23 toys is 276, then what will the price of 12 toys ?
 144
 148
 156
 186
Answer And Explanation
Answer: Option A
Explanation:
Less toys, Less Price (Direct Proportion)
So, let the price be Rs. x
then,
\begin{aligned}
23:12 :: 276:x
=> x = \frac{276*12}{23} \\
=> x = 144
\end{aligned}
So price of 12 toys will be Rs. 144 
4. If a quarter kg of potato costs 60 paise, how many paise will 200gm cost ?
 45 paise
 46 paise
 47 paise
 48 paise
Answer And Explanation
Answer: Option D
Explanation:
Quarter of Kg means 250 gm
Less weight, less price (Direct Proportion)
So,
\begin{aligned}
250:200 :: 60:x \\
=> x = \frac{200*60}{250} \\
=> x = 48
\end{aligned}
So 200 gm will cost 48 paise. 
5. An industrial loom weaves 0.128 metres of cloth every second. Approximately, how many seconds will it take for the loom to weave 25 metre of cloth ?
 194 seconds
 195 seconds
 196 seconds
 197 seconds
Answer And Explanation
Answer: Option B
Explanation:
Let the time required by x seconds.
Then, More cloth means More time (Direct Proportion)
So,
\begin{aligned}
0.128 : 1 :: 25 : x
=> x = \frac{25*1}{0.128} \\
=> x = 195.31
\end{aligned}
So time will be approx 195 seconds 
6. A flagstaff 17.5 metre high casts a shadow of length 40.25 metre. The height of building, which casts a shadow of length 28.75 metre under similar conditions will be :
 12 metre
 12.5 metre
 13.5 metre
 14 metre
Answer And Explanation
Answer: Option B
Explanation:
Less shadow, Less Height (Direct Proportion)
So, let height of building be x metre
then,
\begin{aligned}
40.25 : 17.5 :: 28.75 : x \\
=> x = \frac{17.5*28.75}{40.25} \\
=> x = 12.5
\end{aligned}
So height of building should be 12.5 metre 
7. 36 men can complete a piece of work in 18 days. In how many days will 27 men complete the same work ?
 24 days
 28 days
 34 days
 35 days
Answer And Explanation
Answer: Option A
Explanation:
Less Men, means more Days {Indirect Proportion}
Let the number of days be x
then,
27 : 36 :: 18 : x
[Please pay attention, we have written 27 : 36 rather than 36 : 27, in indirect proportion, if you get it then chain rule is clear to you :)]
\begin{aligned}
x = \frac{36*18}{27} \\
x = 24
\end{aligned}
So 24 days will be required to get work done by 27 men.