If n(A)=1200, n(B)=1250 and n(AintersectionB)=320, then n(AUB) is

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If n(A)=1200, n(B)=1250 and n(AintersectionB)=320, then n(AUB) is

We know that:
n(AUB) = n(A) + n(B) - n(AintersectionB)

Plugging in our given numbers, we get:
n(AUB) = 1200 + 1250 - 320
n(AUB) = 2130