To multiply fractions, multiply the numerators and denominators and reduce if possible. For problem 3, do 7 x 4 = 28. This is the numerator of the answer. The denominator is 8x5 = 40. Therefore, your unreduced fraction is 28/40. Since both 28 and 40 are multiples of 4, you can reduce it to 7/10, since 28/4=7 and 40/4=10. Use this same process for problems 4 through 12.
For problem 13: 2/5= 4/10, so the black box = 1/2. This is because you multiply the numerators and the denominators. Numerators: 4 x 1 = 4. Denominators: 5 x 2 = 10 So, your result fraction is 4/10, which reduces to 2/5. Therefore, the answer is 1/2 ( above math was explanation)
14: multiply the two fractions 6/7 x 4/5 = 24/35, so the answer is 24.
15. Count the shaded squares. There are 25 shaded squares out of 40. The fraction is therefore 25/40 = 5/8. Now count the dotted squares. There are 24 shaded squares out of 40. The fraction is 24/40= 3/5. You could also just look at the far right row to get the same answer because it will reduce anyway, but that might confuse you more.
The answer to 15 is multiplying the two fractions, 5/8 x 3/5.
16. Since both fractions reduce to 1 (numerators are the same as denominators), the model would be 3 boxes by 4 boxes, all shaded and all with dots in the middle.
1,076 (the original thickness) - 22.7 meters (loss per year) * 7 (lost 22.7 meters per year for seven years, so multiply the loss per year by the amount of years) = 917.1 (the size after 7 years)
