# Math Help - Percentages problem – need help adding percentages please

I need 40% overall to pass my exam. So far I have got:

55% of an exam worth 45% of overall grade, and
75% of an essay worth 10% of overall grade

I have one more exam, worth 45% of the overall grade. What is the minimum percentage score I need to achieve to get an overall grade of 40%?

I have no idea how to do the math, so any help is great.

Thanks

Originally Posted by dix
I need 40% overall to pass my exam. So far I have got:

55% of an exam worth 45% of overall grade, and
75% of an essay worth 10% of overall grade

I have one more exam, worth 45% of the overall grade. What is the minimum percentage score I need to achieve to get an overall grade of 40%?

I have no idea how to do the math, so any help is great.

Thanks
Re-write the first percentages as decimal numbers. You'll get:

$0.55 \cdot 45\% + 0.75 \cdot 10\% + x \cdot 45\% = 40\%$

Solve for x and transform into a percentage.

Thanks earboth,

I got:

step 1) (0.55 x 45%) + (0.75 x 10%) + (y x 45%) = 40%
step 2) 0.2475 + 0.075 + (y x 45%) = 40%
step 3) 0.3225 + (y x 45%) = 40%
step 4) 0.40 - 0.3225 = y x 45%
step 5) 0.0775 = y x 45%
step 6) 0.0775 / 0.45 = y
step 7) y = 17.22%

Is that correct? I'd only need around 17%?