Help me with this please & thanks?

Question

if k= -9, evaluate the following

a) 2*k-5

b) 15-k

please show work

1) 3/4+3/10 =

2) 5/7-3/4=

3) 3 and 3/5 - 7 and 1/8

Answer 1

a) 2*k-5 = 2(-9) - 5 = -18 - 5 = - 23

b) 15-k = 15 -(-9) = 15 + 9 = 24

1) 3/4+3/10 = (3/4)(10/10) + (3/10)(4/4) = 30/40 + 12/40 = 42/40 = 21/20 = 1 1/20

2) 5/7-3/4= (5/7)(4/4) - (3/4)(7/7) = 20/28 - 21/28 = -1/28

3) 3 3/5 - 7 1/8 = 18/5 - 57/8 = (18/5)(8/8) - (57/8)(5/5) = 144/40 - 285/40 = - 141/40 = - 3 21/40

Answer 2

2k - 5

2 (-9) - 5

-18 -5

-23

¯¯¯¯

15 - k

15 - (-9)

15 + 9

24

¯¯¯¯

3/4 + 3/10

15/20 + 6/20

(15 + 6) / 20

21/20

1  1/20

¯¯¯¯¯¯¯

5/7 - 3/4

20/28 - 21/28

(20 - 21) / 28

-1/28

¯¯¯¯¯

3 3/5 - 7 1/8

18/5 - 57/8

144/40 - 285/40

(144 - 285) / 40

-141/40

-3  21/40

¯¯¯¯¯¯¯¯¯

Answer 3

a

2x-9 is -(2x9)

so it will be -18-5= -23

b

15 - - 9

negatives cancel out

so it will be 15 + 9=24

1

3/4+ 3/10

LCM (least common multiple) of 4 and 10 is 20

change denominators (number on bottom) to 20 by multiplying by whats needed with 4 it is 5, with 10 it is 2

it is important that you don't change the actual value

(2/2 =1, multiplying by 1 does not change the actual value)

so it will be 3x5/4x5 + 3x2/10x2= 15/20 + 6/20= 21/20

2

5/7 - 3/4

LCM of 7 and 4 is 28

7 needs 4 and 4 needs 7

so it will be 5x4/7x4 - 3x7/4x7= 20/28 - 21/28= -1/28

3

3 and 3/5 - 7 and 1/8

3 and 3/5 is actually 18/5 and 7 and 1/8 is 57/8

LCM (its big but no worries) is 40

18x8/5x8 - 57x5/8x5= 144/40 - 285/40= -141/40 or -3 and 21/40

Answer 4

a)

=(2*-9)-5

=-18-5

=-23

b)

=15-(-9)

=15+9

=24

1)

=(30+12)/40

=42/40

=21/20

2)

=(20-21)/28

=-1/28

3)

=18/5 - 57/8

=(144-285)/40

=-141/40

Answer 5

a) -9 -5 = -14

2 x -14 = -28

b) 15 - (-9) = 24

1) set denominator to 20:

15/20 + 6/20 = 21/20

2) set denominator to 28:

20/28 -21/28 = -1/28

3) 18/5 -57/8

set denominator to 40:

144/40 - 285/40 = -141/40

oops! Looks like I misread the first one