A = C + 2.85
B = A - 3.2 = C + 2.85 - 3.2 = C - 0.35

A + B + C = 22.3

C + 2.85 + C - 0.35 + C = 22.3
3 x C + 2.5 = 22.3
3 x C = 22.3 - 2.5 = 19.8

C = 19.8 ÷ 3 = 6.6


Or you can change them all into parcel A first.


Change parcel B to parcel A, total mass goes up by 3.2 kg
Change parcel C to A, total mass goes up by 2.85 kg

Total mass now
= 22.3kg + 3.2kg + 2.85kg
= 28.35kg

Now we have 3 of parcel A.

1 parcel A's mass = 28.35kg ÷ 3 = 9.45kg

Since parcel C is 2.85kg lighter than Parcel A,

Parcel C's mass = 9.45kg - 2.85kg
= 6.6kg

IF B is 1 kg (say, IF)

THEN A is 4.2 kg

AND C is 1.35 kg

THUS, total is 6.55 kg

HOWEVER, qn says total is 22.3 kg,
NOT 6.55 kg

WHICH means the difference is 15.75kg

SO this means
A CANNOT be 4.2 kg
B CANNOT be 1 kg
C CANNOT be 1.35 kg

HENCE, spread the difference of
15.75 kg over the 3 parcels,
we get 5.25 kg

THEREFORE, we know mass of C is
5.25+1.35 = 6.60 kg


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