Answer:
5
Step-by-step explanation:
Let x be the number of cell phones with keyboards needed.
40% = [tex]\frac{40}{100}[/tex]
[tex]\frac{x+45}{x+120}[/tex] = [tex]\frac{40}{100}[/tex]
x+45 = 40 -----1
x+120 = 100 -----2
You would want to make the total of 1 the same as 2.
1×[tex]\frac{100}{40}[/tex]: 2.5+112.5 = 100 -----3
Now 2 and 3 are equal.
x+120 = 2.5x+112.5
Isolate the x and numbers.
120-112.5 = 2.5x-x
Simplify.
1.5x = 7.5
x = [tex]\frac{1}{1.5}[/tex] × 7.5
x = 5
The manager of the store needs to add 5 more cell phones with keyboards.
