Answer:
Step-by-step explanation:
Question (1). An alloy contains zinc and copper in the ratio of 7 : 9.
If the weight of an alloy = x kgs
Then weight of copper = ![\frac{9}{7+9}\times (x)](https://tex.z-dn.net/?f=%5Cfrac%7B9%7D%7B7%2B9%7D%5Ctimes%20%28x%29)
= ![\frac{9}{16}\times (x)](https://tex.z-dn.net/?f=%5Cfrac%7B9%7D%7B16%7D%5Ctimes%20%28x%29)
And the weight of zinc = ![\frac{7}{7+9}\times (x)](https://tex.z-dn.net/?f=%5Cfrac%7B7%7D%7B7%2B9%7D%5Ctimes%20%28x%29)
= ![\frac{7}{16}\times (x)](https://tex.z-dn.net/?f=%5Cfrac%7B7%7D%7B16%7D%5Ctimes%20%28x%29)
If the weight of zinc = 31.5 kg
31.5 = ![\frac{7}{16}\times (x)](https://tex.z-dn.net/?f=%5Cfrac%7B7%7D%7B16%7D%5Ctimes%20%28x%29)
x = ![\frac{16\times 31.5}{7}](https://tex.z-dn.net/?f=%5Cfrac%7B16%5Ctimes%2031.5%7D%7B7%7D)
x = 72 kgs
Therefore, weight of copper = ![\frac{9}{16}\times (72)](https://tex.z-dn.net/?f=%5Cfrac%7B9%7D%7B16%7D%5Ctimes%20%2872%29)
= 40.5 kgs
2). i). 2 : 3 = ![\frac{2}{3}](https://tex.z-dn.net/?f=%5Cfrac%7B2%7D%7B3%7D)
4 : 5 = ![\frac{4}{5}](https://tex.z-dn.net/?f=%5Cfrac%7B4%7D%7B5%7D)
Now we will equalize the denominators of each fraction to compare the ratios.
= ![\frac{10}{15}](https://tex.z-dn.net/?f=%5Cfrac%7B10%7D%7B15%7D)
![\frac{4}{5}\times \frac{3}{3}=\frac{12}{15}](https://tex.z-dn.net/?f=%5Cfrac%7B4%7D%7B5%7D%5Ctimes%20%5Cfrac%7B3%7D%7B3%7D%3D%5Cfrac%7B12%7D%7B15%7D)
Since, ![\frac{12}{15}>\frac{10}{15}](https://tex.z-dn.net/?f=%5Cfrac%7B12%7D%7B15%7D%3E%5Cfrac%7B10%7D%7B15%7D)
Therefore, 4 : 5 > 2 : 3
ii). 11 : 19 = ![\frac{11}{19}](https://tex.z-dn.net/?f=%5Cfrac%7B11%7D%7B19%7D)
19 : 21 = ![\frac{19}{21}](https://tex.z-dn.net/?f=%5Cfrac%7B19%7D%7B21%7D)
By equalizing denominators of the given fractions,
![\frac{11}{19}\times \frac{21}{21}=\frac{231}{399}](https://tex.z-dn.net/?f=%5Cfrac%7B11%7D%7B19%7D%5Ctimes%20%5Cfrac%7B21%7D%7B21%7D%3D%5Cfrac%7B231%7D%7B399%7D)
And ![\frac{19}{21}\times \frac{19}{19}=\frac{361}{399}](https://tex.z-dn.net/?f=%5Cfrac%7B19%7D%7B21%7D%5Ctimes%20%5Cfrac%7B19%7D%7B19%7D%3D%5Cfrac%7B361%7D%7B399%7D)
Since, ![\frac{361}{399}>\frac{231}{399}](https://tex.z-dn.net/?f=%5Cfrac%7B361%7D%7B399%7D%3E%5Cfrac%7B231%7D%7B399%7D)
Therefore, 19 : 21 > 11 : 19
iii). ![\frac{1}{2}:\frac{1}{3}=\frac{1}{2}\times \frac{3}{1}](https://tex.z-dn.net/?f=%5Cfrac%7B1%7D%7B2%7D%3A%5Cfrac%7B1%7D%7B3%7D%3D%5Cfrac%7B1%7D%7B2%7D%5Ctimes%20%5Cfrac%7B3%7D%7B1%7D)
![=\frac{3}{2}](https://tex.z-dn.net/?f=%3D%5Cfrac%7B3%7D%7B2%7D)
![\frac{1}{3}:\frac{1}{4}=\frac{1}{3}\times \frac{4}{1}](https://tex.z-dn.net/?f=%5Cfrac%7B1%7D%7B3%7D%3A%5Cfrac%7B1%7D%7B4%7D%3D%5Cfrac%7B1%7D%7B3%7D%5Ctimes%20%5Cfrac%7B4%7D%7B1%7D)
= ![\frac{4}{3}](https://tex.z-dn.net/?f=%5Cfrac%7B4%7D%7B3%7D)
Now we equalize the denominators of the fractions,
![\frac{3}{2}\times \frac{3}{3}=\frac{9}{6}](https://tex.z-dn.net/?f=%5Cfrac%7B3%7D%7B2%7D%5Ctimes%20%5Cfrac%7B3%7D%7B3%7D%3D%5Cfrac%7B9%7D%7B6%7D)
And ![\frac{4}{3}\times \frac{2}{2}=\frac{8}{6}](https://tex.z-dn.net/?f=%5Cfrac%7B4%7D%7B3%7D%5Ctimes%20%5Cfrac%7B2%7D%7B2%7D%3D%5Cfrac%7B8%7D%7B6%7D)
Since ![\frac{9}{6}>\frac{8}{6}](https://tex.z-dn.net/?f=%5Cfrac%7B9%7D%7B6%7D%3E%5Cfrac%7B8%7D%7B6%7D)
Therefore,
will be the answer.
IV). ![1\frac{1}{5}:1\frac{1}{3}=\frac{6}{5}:\frac{4}{3}](https://tex.z-dn.net/?f=1%5Cfrac%7B1%7D%7B5%7D%3A1%5Cfrac%7B1%7D%7B3%7D%3D%5Cfrac%7B6%7D%7B5%7D%3A%5Cfrac%7B4%7D%7B3%7D)
![=\frac{6}{5}\times \frac{3}{4}](https://tex.z-dn.net/?f=%3D%5Cfrac%7B6%7D%7B5%7D%5Ctimes%20%5Cfrac%7B3%7D%7B4%7D)
![=\frac{18}{20}](https://tex.z-dn.net/?f=%3D%5Cfrac%7B18%7D%7B20%7D)
![=\frac{9}{10}](https://tex.z-dn.net/?f=%3D%5Cfrac%7B9%7D%7B10%7D)
Similarly, ![\frac{2}{5}:\frac{3}{2}=\frac{2}{5}\times \frac{2}{3}](https://tex.z-dn.net/?f=%5Cfrac%7B2%7D%7B5%7D%3A%5Cfrac%7B3%7D%7B2%7D%3D%5Cfrac%7B2%7D%7B5%7D%5Ctimes%20%5Cfrac%7B2%7D%7B3%7D)
By equalizing the denominators,
![\frac{9}{10}\times \frac{30}{30}=\frac{270}{300}](https://tex.z-dn.net/?f=%5Cfrac%7B9%7D%7B10%7D%5Ctimes%20%5Cfrac%7B30%7D%7B30%7D%3D%5Cfrac%7B270%7D%7B300%7D)
Similarly, ![\frac{4}{15}\times \frac{20}{20}=\frac{80}{300}](https://tex.z-dn.net/?f=%5Cfrac%7B4%7D%7B15%7D%5Ctimes%20%5Cfrac%7B20%7D%7B20%7D%3D%5Cfrac%7B80%7D%7B300%7D)
Since ![\frac{270}{300}>\frac{80}{300}](https://tex.z-dn.net/?f=%5Cfrac%7B270%7D%7B300%7D%3E%5Cfrac%7B80%7D%7B300%7D)
Therefore, ![1\frac{1}{5}:1\frac{1}{3}>\frac{2}{5}:\frac{3}{2}](https://tex.z-dn.net/?f=1%5Cfrac%7B1%7D%7B5%7D%3A1%5Cfrac%7B1%7D%7B3%7D%3E%5Cfrac%7B2%7D%7B5%7D%3A%5Cfrac%7B3%7D%7B2%7D)
V). If a : b = 6 : 5
![\frac{a}{b}=\frac{6}{5}](https://tex.z-dn.net/?f=%5Cfrac%7Ba%7D%7Bb%7D%3D%5Cfrac%7B6%7D%7B5%7D)
![=\frac{6}{5}\times \frac{2}{2}](https://tex.z-dn.net/?f=%3D%5Cfrac%7B6%7D%7B5%7D%5Ctimes%20%5Cfrac%7B2%7D%7B2%7D)
![=\frac{12}{10}](https://tex.z-dn.net/?f=%3D%5Cfrac%7B12%7D%7B10%7D)
And b : c = 10 : 9
![\frac{b}{c}=\frac{10}{9}](https://tex.z-dn.net/?f=%5Cfrac%7Bb%7D%7Bc%7D%3D%5Cfrac%7B10%7D%7B9%7D)
Since a : b = 12 : 10
And b : c = 10 : 9
Since b = 10 is common in both the ratios,
Therefore, combined form of the ratios will be,
a : b : c = 12 : 10 : 9