20. Gunpowder contains 75% nitre and 10% sulphur. Find the amount of gunpowder which
carries 9 kg nitre. What amount of gunpowder would contain 2.5 kg sulphur?
21. Divide 7000 among A, B and C such that A gets 50% of what B gets and B gets 50% of what C gets.
22. Find the percentage of pure gold in 22-carat gold, if 24-carat gold is 100% pure.
23. The salary of an officer is increased by 25%. By what per cent should the new salary be
decreased to restore the original salary?
Answers
Answer:
20.Let x kg be the amount of gunpowder which carries 9 kg nitre. Because gunpowder contains 75% nitre we can say:
x * 0.75 = 9
x = 9 / 0.75
x = 12.
Hence 12 kg gunpowder carries 9 kg nitre.
Let y kg be the amount of gunpowder which contains 2.5 kg sulfur. As gunpowder contains 10% sulfur we obtain:
y * 0.1 = 2.5
y = 25.
21.So we can consider here that C gets the maximum
order goes like
C > B > A
Let us assume
C = 4x
thus B = 2x ( 50% of C = 1/2 C )
Thus A = x ( 50% of B = 1/2 B )
equation gives
x + 2x + 4x = 7000
7x = 7000
thus x = 1000
A = 1000
B = 2000
C = 4000
22. 22 carat gold contains 91.66% of pure form of gold.
24 carat gold is 100% pure form of gold.
Percentage of pure gold.
Consider 24 carat gold as 24 segments of gold which equals 100% of gold.
24 segments of gold = 100%
1 segment of gold
1 segment gold contains 4.16% of pure form of gold
Hence, 22 carat of gold contains 22 segments of gold,
23.Let's consider the salary of officer to be 100.
So, If the salary is increased by 25% , then the new salary -
100+ [100×(25/100) ] = 100+25 = 125
So, his new salary is 125
To make his salary original 25 must be subtracted from 125 , then his salary will be 125-25 = 100 or original salary.
So, To find percentage of salary which must be decreased we must find that 25 is what percentage of 125 .
So, decrease%
= (25/125) × 100
= 1/5 × 100
= 20%
Answer) 20% of his new salary must be deducted so that his salary becomes Original.