Question

The sum of three numbers is 8. The third is 9
less than 8 times the second. 10 times the
first is 7 less than 8 times the second. Find
the numbers.

Answer 1

Answer:

→ First value is 1

→ Second value is 2

→ Third value is 5

Step-by-step explanation:

• let numbers be x, y and z

${ \tt{z = 8y - 9 - - - (eqn \: 1)}} \\ \\ { \tt{10x = 8y - 7 - - - (eqn \: 2)}} \\ \\ { \tt{x + y + z = 8 - - - (eqn \: 3)}}$

• from eqn 2, make x the subject:

${ \tt{x = \frac{8y - 7}{10} }}$

• substitute all variables in eqn 3:

${ \tt{ \frac{8y - 7}{10} + y + 8y - 9 = 8}} \\ \\ { \tt{8y - 7 + 10y + 80y - 90 = 80}} \\ \\ { \tt{98y = 177}} \\ \\ { \boxed{ \tt{ \: y = 1.8}}}$

• find z

${ \tt{z = 8y - 9}} \\ \\ { \tt{z = 8(1.8) - 9}} \\ \\ { \tt{z = 14.4 - 9}} \\ \\ { \boxed{ \tt{ \: z = 5.4 \: }}}$

• find x:

${ \tt{x = \frac{8(1.8) - 7}{10} }} \\ \\ { \tt{x = \frac{7.4}{10} }} \\ \\ { \boxed{ \tt{ \: x = 0.74 \: }}}$

Rounding to nearest value:

${ \boxed{ \rm{x = 1}}} \\ { \boxed{ \rm{y =2 }}} \\ { \boxed{ \rm{z = 5}}}$