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**Calculating the rest mass of Ra [simple!!]**

## Homework Statement

Calculate the rest mass of 226/88 Ra.

## Homework Equations

## The Attempt at a Solution

There are 88 protons and 138 neutrons.

Therefore, (88*1.007276)+(138*1.008665)=227.8361u

But the answer says 226.0254u.

It also says 4/2 He is 4.0026u while my calculation is 4.0319u.

HELP~