Divanna scored 67% on her last test, If she had paid closer attention to signs, she would have had 2 more problems right and would have scored 80%. Write the expression for how many problems in all she would have answered correctly.

Answer 1

let n = # questions answered
let N = total questions

n/N = .67
(n+2)/N = .8

so,

n/.67 = (n+2)/.8
.8n = .67n + 1.3
.13n = 1.3
n = 10

so, she answered 10/15 = 67%
by answering 2 more, she'd have had 12/15 = 80%