(1) 160 pupils' admission fees = $160 x 3.5 = $560

take that from total: $(5120 - 560) = $4560

Now, $(8.5 + 3.5) = $12

and, $4560 / $12 = 380

i.e, 380 adults and (380 + 160) = 540 pupils visited the exhibition.

(2) (a) price of 1 mango (1u) = 4 x price of a mango (4u)

a mango cost $2.10 more than an orange

that would mean 3u = 2.10

and so, 1u = 0.70

thus, a mango cost $2.80 and an orange $0.70

(b) 8 mangoes cost $2.8 x 8 = $22.40

thus, $(30.80 - 22.40) = $8.20 was the cost of oranges

so that, no. of oranges = $8.4 / $0.7 = 12

therefore, fraction of oranges = 12/20 = 3/5