Question

if 3 kg of sugar and 4 kg of flour cost $6.80 while 2 kg of sugar and 7 kg of flour cost $8.00. find the total cost of 6 kg of sugar and 5 kg of flour

Give answer quickly using two variables and show solution​

Answer 1

Answer:

      $ 11.2

Step-by-step explanation:

let sugar be 'x'

let flour be 'y'

3x + 4y = 6.8

3x = 6.8 - 4y

x = 6.8 - 4y / 3 -------{i}

2x + 7y = 8 -------{ii}

from {i} and {ii}

2 [6.8 - 4y / 3] + 7y = 8

2 [6.8 - 4y / 3] + [3×7y / 3] = [3 × 8 / 3]

2 [6.8 - 4y] + [3×7y]  = [3 × 8]

13.6 - 8y + 21y = 24

13y = 24 - 13.6

13y = 10.4

y = 10.4 / 13

y = 0.8

x = 6.8 - 4y / 3

x = 6.8 - 4×0.8 / 3

x = 6.8 - 3.2 / 3

x = 3.6 / 3

x = 1.2

total cost of 6 kg of sugar and 5 kg of flour

= 6x + 5y

= (6×1.2) + (5×0.8)

= 7.2 + 4

= $ 11.2