Question

2.12 Find the value of x in the following proportions
(i) 7:14: :15 :
(ii) x :8::8:16​

Answer 1

Answer

7:14::15:x

7/14 = 15/x

by cross multiplication

7x = 14×15

7x = 210/7

x = 30

x:8::8:16

x/8 = 8/16

by cross multiplication

8÷8 = 1

So value of x = 16

Answer 2

• ${\sf{\bold{(í)\:7:\:14\::\::\:15\::\:x}}}$

${ }$

$:\:\Longrightarrow{\sf{\pink{By\:Cross\:Multiplication}}}$

${ }$

$:\:\Longrightarrow{\sf{7x\:=\:14\:༝\:15}}$

${ }$

$:\:\Longrightarrow{\sf{x\:=\:}}{\sf{\frac{14\:༝\:15}{7}}}$

${ }$

$:\:\Longrightarrow{\underline{\boxed{\bold{\sf{x\:=\:30}}}}}\:★$

━━━━━━━━━━━━━━━━━━━━━━━━

• ${\sf{\bold{(íí)\:x:\:8\::\::\:8\::\:16}}}$

${ }$

$:\:\Longrightarrow{\sf{\pink{By\:Cross\:Multiplication}}}$

${ }$

$:\:\Longrightarrow{\sf{16x\:=\:8\:༝\:8}}$

${ }$

$:\:\Longrightarrow{\sf{x\:=\:}}{\sf{\frac{8\:༝\:8}{16}}}$

${ }$

$:\:\Longrightarrow{\underline{\boxed{\bold{\sf{x\:=\:4}}}}}\:★$