What number should go in the space? Multiplying by 1.15 is the same as increasing by _____%.

7 hours 12 minutes
6 hours 46 minutes
6 hours 53 minutes
--------------------------sum
Total: 19 hours 111 minutes, which converts to (19 × 60) + 111 = 1140 + 111 = 1251 minutes

Calculate average time by dividing by 3: 1251 / 3 = 417 minutes, equivalent to 6 hours 57 minutes, which is the average delivery duration.

Answer:

(1) The necessary proportion of spirit to varnish stands at 1:3.

(2) A total of 80 ml of mineral spirit is required.

(3) The ratio of the heights to the widths of the tapestries is 3:2.

Step-by-step explanation:

(1) To achieve a mixture containing 25% mineral spirit, the blend consists of 25% spirit and 75% varnish.

Therefore,

Consequently, the proportion of spirit to varnish is 1:3.

(2) Using 240ml of varnish indicates this is 75% of the entire solution, which means the ratio of varnish to the total solution is 3:4.

Let the total solution quantity be .

Thus, .

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This means the total solution amounts to 320 ml.

Now, calculating Spirit = Total solution - Varnish

⇒Spirit = 320ml-240ml

⇒Spirit = 80ml

Therefore, when using 240 ml of varnish, you will require 80 ml of mineral spirit.

(3) The dimensions of Robison's tapestries are uniform at 1.5m in length and 1m in width. Initially, to obtain whole numbers, we multiply these dimensions by 10.

Thus, the dimensions become 15m long and 10m wide.

Now, the proportion of Height to Width is 15:10

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Thus, the proportion of the heights of the tapestries to their widths is 3:2.