Roberto comprou 2 cadernos a R$12,40 cada duas borrachas a R$0,80 centavos cada uma meia dúzia de lápis a R$0,60 centavos e meia dezena de canetas a R$2,10. Se Roberto tinha apenas uma nota de R$50,00quanto recebeu de troco?

3-4

step-by-step explanation:

the answer is 3-4 because both 45 and 60 has a multiple of 15.

45/3=15

60/4=15

therefore the odds against selecting a red is 4-3

we have three similar triangles, because each has a right angle and shares an angle.   let's write the angles in order: opposite to short leg, long leg, hypotenuse.

cab similar to bad similar to cbd

or as ratios,

ca: ab: cb = ba: ad: bd = cb: bd: cd

we also know

ac = ad + cd

(ad+cd): ab: cb = ba: ad: bd = cb: bd: cd

(ad+cd)/cb=cb/cd

we have cb=6, ad=5 and seek x=cd.

we reject the negative root and conclude x=4

answer: 4

not sure but it may be b, as i said i'm not sure.

it is 10.6 according to my calculations